7.4 Querying with GORM 3.1.4

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(Quick Reference) # 7.4 Querying with GORM - Reference Documentation Authors: Graeme Rocher, Peter Ledbrook, Marc Palmer, Jeff Brown, Luke Daley, Burt Beckwith, Lari Hotari Version: 3.1.4 ## Table of Contents ## 7.4 Querying with GORM GORM supports a number of powerful ways to query from dynamic finders, to criteria to Hibernate's object oriented query language HQL. Depending on the complexity of the query you have the following options in order of flexibility and power: Dynamic Finders Where Queries Criteria Queries Hibernate Query Language (HQL) In addition, Groovy's ability to manipulate collections with GPath and methods like sort, findAll and so on combined with GORM results in a powerful combination. However, let's start with the basics. #### Listing instances Use the list method to obtain all instances of a given class:
    def books = Book.list()
The list method supports arguments to perform pagination:
    def books = Book.list(offset:10, max:20)
as well as sorting:
    def books = Book.list(sort:"title", order:"asc")
Here, the `sort` argument is the name of the domain class property that you wish to sort on, and the `order` argument is either `asc` for ascending or `desc` for descending. #### Retrieval by Database Identifier The second basic form of retrieval is by database identifier using the get method:
    def book = Book.get(23)
You can also obtain a list of instances for a set of identifiers using getAll:
    def books = Book.getAll(23, 93, 81)
## 7.4.1 Dynamic Finders GORM supports the concept of dynamic finders. A dynamic finder looks like a static method invocation, but the methods themselves don't actually exist in any form at the code level. Instead, a method is auto-magically generated using code synthesis at runtime, based on the properties of a given class. Take for example the `Book` class:
    class Book {
        String title
        Date releaseDate
        Author author
    }
    class Author {
        String name
    }
The `Book` class has properties such as `title`, `releaseDate` and `author`. These can be used by the findBy and findAllBy methods in the form of "method expressions":

    def book = Book.findByTitle("The Stand")book = Book.findByTitleLike("Harry Pot%")book = Book.findByReleaseDateBetween(firstDate, secondDate)book = Book.findByReleaseDateGreaterThan(someDate)book = Book.findByTitleLikeOrReleaseDateLessThan("%Something%", someDate)
#### Method Expressions A method expression in GORM is made up of the prefix such as findBy followed by an expression that combines one or more properties. The basic form is:
    Book.findBy([Property][Comparator][Boolean Operator])?[Property][Comparator]
The tokens marked with a '?' are optional. Each comparator changes the nature of the query. For example:

    def book = Book.findByTitle("The Stand")book =  Book.findByTitleLike("Harry Pot%")
In the above example the first query is equivalent to equality whilst the latter, due to the `Like` comparator, is equivalent to a SQL `like` expression. The possible comparators include: `InList` - In the list of given values `LessThan` - less than a given value `LessThanEquals` - less than or equal a give value `GreaterThan` - greater than a given value `GreaterThanEquals` - greater than or equal a given value `Like` - Equivalent to a SQL like expression `Ilike` - Similar to a `Like`, except case insensitive `NotEqual` - Negates equality `InRange` - Between the `from` and `to` values of a Groovy Range `Rlike` - Performs a Regexp LIKE in MySQL or Oracle otherwise falls back to `Like` `Between` - Between two values (requires two arguments) `IsNotNull` - Not a null value (doesn't take an argument) `IsNull` - Is a null value (doesn't take an argument) Notice that the last three require different numbers of method arguments compared to the rest, as demonstrated in the following example:

    def now = new Date()
    def lastWeek = now - 7
    def book = Book.findByReleaseDateBetween(lastWeek, now)books = Book.findAllByReleaseDateIsNull()
    books = Book.findAllByReleaseDateIsNotNull()
#### Boolean logic (AND/OR) Method expressions can also use a boolean operator to combine two or more criteria:
    def books = Book.findAllByTitleLikeAndReleaseDateGreaterThan(
                          "%Java%", new Date() - 30)
In this case we're using `And` in the middle of the query to make sure both conditions are satisfied, but you could equally use `Or`:
    def books = Book.findAllByTitleLikeOrReleaseDateGreaterThan(
                          "%Java%", new Date() - 30)
You can combine as many criteria as you like, but they must all be combined with `And` or all `Or`. If you need to combine `And` and `Or` or if the number of criteria creates a very long method name, just convert the query to a Criteria or HQL query. #### Querying Associations Associations can also be used within queries:

    def author = Author.findByName("Stephen King")def books = author ? Book.findAllByAuthor(author) : []
In this case if the `Author` instance is not null we use it in a query to obtain all the `Book` instances for the given `Author`. #### Pagination and Sorting The same pagination and sorting parameters available on the list method can also be used with dynamic finders by supplying a map as the final parameter:
    def books = Book.findAllByTitleLike("Harry Pot%",
                   [max: 3, offset: 2, sort: "title", order: "desc"])
## 7.4.2 Where Queries The `where` method, introduced in Grails 2.0, builds on the support for Detached Criteria by providing an enhanced, compile-time checked query DSL for common queries. The `where` method is more flexible than dynamic finders, less verbose than criteria and provides a powerful mechanism to compose queries. #### Basic Querying The `where` method accepts a closure that looks very similar to Groovy's regular collection methods. The closure should define the logical criteria in regular Groovy syntax, for example:
    def query = Person.where {
       firstName == "Bart"
    }
    Person bart = query.find()
The returned object is a `DetachedCriteria` instance, which means it is not associated with any particular database connection or session. This means you can use the `where` method to define common queries at the class level:
    class Person {
        static simpsons = where {
             lastName == "Simpson"
        }
        …
    }
    …
    Person.simpsons.each {
        println it.firstname
    }
Query execution is lazy and only happens upon usage of the DetachedCriteria instance. If you want to execute a where-style query immediately there are variations of the `findAll` and `find` methods to accomplish this:
    def results = Person.findAll {
         lastName == "Simpson"
    }
    def results = Person.findAll(sort:"firstName") {
         lastName == "Simpson"
    }
    Person p = Person.find { firstName == "Bart" }
Each Groovy operator maps onto a regular criteria method. The following table provides a map of Groovy operators to methods:
Operator | Criteria Method | Description
--- | --- | ---
== | eq | Equal to
!= | ne | Not equal to
> | gt | Greater than
< | lt | Less than
>= | ge | Greater than or equal to
<= | le | Less than or equal to
in | inList | Contained within the given list
==~ | like | Like a given string
=~ | ilike | Case insensitive like
It is possible use regular Groovy comparison operators and logic to formulate complex queries:
    def query = Person.where {
        (lastName != "Simpson" && firstName != "Fred") || (firstName == "Bart" && age > 9)
    }
    def results = query.list(sort:"firstName")
The Groovy regex matching operators map onto like and ilike queries unless the expression on the right hand side is a `Pattern` object, in which case they map onto an `rlike` query:
    def query = Person.where {
         firstName ==~ ~/B.+/
    }
Note that `rlike` queries are only supported if the underlying database supports regular expressions A `between` criteria query can be done by combining the `in` keyword with a range:
    def query = Person.where {
         age in 18..65
    }
Finally, you can do `isNull` and `isNotNull` style queries by using `null` with regular comparison operators:
    def query = Person.where {
         middleName == null
    }
#### Query Composition Since the return value of the `where` method is a DetachedCriteria instance you can compose new queries from the original query:
    def query = Person.where {
         lastName == "Simpson"
    }
    def bartQuery = query.where {
         firstName == "Bart"
    }
    Person p = bartQuery.find()
Note that you cannot pass a closure defined as a variable into the `where` method unless it has been explicitly cast to a `DetachedCriteria` instance. In other words the following will produce an error:
    def callable = {
        lastName == "Simpson"
    }
    def query = Person.where(callable)
The above must be written as follows:

    import grails.gorm.DetachedCriteriadef callable = {
        lastName == "Simpson"
    } as DetachedCriteria<Person>
    def query = Person.where(callable)
As you can see the closure definition is cast (using the Groovy `as` keyword) to a DetachedCriteria instance targeted at the `Person` class. #### Conjunction, Disjunction and Negation As mentioned previously you can combine regular Groovy logical operators (`||` and `&&`) to form conjunctions and disjunctions:
    def query = Person.where {
        (lastName != "Simpson" && firstName != "Fred") || (firstName == "Bart" && age > 9)
    }
You can also negate a logical comparison using `!`:
    def query = Person.where {
        firstName == "Fred" && !(lastName == 'Simpson')
    }
#### Property Comparison Queries If you use a property name on both the left hand and right side of a comparison expression then the appropriate property comparison criteria is automatically used:
    def query = Person.where {
       firstName == lastName
    }
The following table described how each comparison operator maps onto each criteria property comparison method:
Operator | Criteria Method | Description
--- | --- | ---
== | eqProperty | Equal to
!= | neProperty | Not equal to
> | gtProperty | Greater than
< | ltProperty | Less than
>= | geProperty | Greater than or equal to
<= | leProperty | Less than or equal to
#### Querying Associations Associations can be queried by using the dot operator to specify the property name of the association to be queried:
    def query = Pet.where {
        owner.firstName == "Joe" || owner.firstName == "Fred"
    }
You can group multiple criterion inside a closure method call where the name of the method matches the association name:
    def query = Person.where {
        pets { name == "Jack" || name == "Joe" }
    }
This technique can be combined with other top-level criteria:
    def query = Person.where {
         pets { name == "Jack" } || firstName == "Ed"
    }
For collection associations it is possible to apply queries to the size of the collection:
    def query = Person.where {
           pets.size() == 2
    }
The following table shows which operator maps onto which criteria method for each size() comparison:
Operator | Criteria Method | Description
--- | --- | ---
== | sizeEq | The collection size is equal to
!= | sizeNe | The collection size is not equal to
> | sizeGt | The collection size is greater than
< | sizeLt | The collection size is less than
>= | sizeGe | The collection size is greater than or equal to
<= | sizeLe | The collection size is less than or equal to
#### Subqueries It is possible to execute subqueries within where queries. For example to find all the people older than the average age the following query can be used:
    final query = Person.where {
      age > avg(age)
    }
The following table lists the possible subqueries:
Method | Description
--- | ---
avg | The average of all values
sum | The sum of all values
max | The maximum value
min | The minimum value
count | The count of all values
property | Retrieves a property of the resulting entities
You can apply additional criteria to any subquery by using the `of` method and passing in a closure containing the criteria:
    def query = Person.where {
      age > avg(age).of { lastName == "Simpson" } && firstName == "Homer"
    }
Since the `property` subquery returns multiple results, the criterion used compares all results. For example the following query will find all people younger than people with the surname "Simpson":
    Person.where {
        age < property(age).of { lastName == "Simpson" }
    }
#### More Advanced Subqueries in GORM The support for subqueries has been extended. You can now use in with nested subqueries
    def results = Person.where {
        firstName in where { age < 18 }.firstName
    }.list()
Criteria and where queries can be seamlessly mixed:
    def results = Person.withCriteria {
        notIn "firstName", Person.where { age < 18 }.firstName
     }
Subqueries can be used with projections:
    def results = Person.where {
        age > where { age > 18 }.avg('age')
    }
Correlated queries that span two domain classes can be used:
    def employees = Employee.where {
        region.continent in ['APAC', "EMEA"]
        }.id()
        def results = Sale.where {
        employee in employees && total > 100000
        }.employee.list()
And support for aliases (cross query references) using simple variable declarations has been added to where queries:
    def query = Employee.where {
        def em1 = Employee
        exists Sale.where {
            def s1 = Sale
            def em2 = employee
            return em2.id == em1.id
        }.id()
    }
    def results = query.list()
#### Other Functions There are several functions available to you within the context of a query. These are summarized in the table below:
Method | Description
--- | ---
second | The second of a date property
minute | The minute of a date property
hour | The hour of a date property
day | The day of the month of a date property
month | The month of a date property
year | The year of a date property
lower | Converts a string property to upper case
upper | Converts a string property to lower case
length | The length of a string property
trim | Trims a string property
Currently functions can only be applied to properties or associations of domain classes. You cannot, for example, use a function on a result of a subquery. For example the following query can be used to find all pet's born in 2011:
    def query = Pet.where {
        year(birthDate) == 2011
    }
You can also apply functions to associations:
    def query = Person.where {
        year(pets.birthDate) == 2009
    }
#### Batch Updates and Deletes Since each `where` method call returns a DetachedCriteria instance, you can use `where` queries to execute batch operations such as batch updates and deletes. For example, the following query will update all people with the surname "Simpson" to have the surname "Bloggs":
    def query = Person.where {
        lastName == 'Simpson'
    }
    int total = query.updateAll(lastName:"Bloggs")
Note that one limitation with regards to batch operations is that join queries (queries that query associations) are not allowed. To batch delete records you can use the `deleteAll` method:
    def query = Person.where {
        lastName == 'Simpson'
    }
    int total = query.deleteAll()
## 7.4.3 Criteria Criteria is an advanced way to query that uses a Groovy builder to construct potentially complex queries. It is a much better approach than building up query strings using a `StringBuffer`. Criteria can be used either with the createCriteria or withCriteria methods. The builder uses Hibernate's Criteria API. The nodes on this builder map the static methods found in the Restrictions class of the Hibernate Criteria API. For example:
    def c = Account.createCriteria()
    def results = c {
        between("balance", 500, 1000)
        eq("branch", "London")
        or {
            like("holderFirstName", "Fred%")
            like("holderFirstName", "Barney%")
        }
        maxResults(10)
        order("holderLastName", "desc")
    }
This criteria will select up to 10 `Account` objects in a List matching the following criteria: `balance` is between 500 and 1000 `branch` is 'London' `holderFirstName` starts with 'Fred' or 'Barney' The results will be sorted in descending order by `holderLastName`. If no records are found with the above criteria, an empty List is returned. #### Conjunctions and Disjunctions As demonstrated in the previous example you can group criteria in a logical OR using an `or { }` block:
    or {
        between("balance", 500, 1000)
        eq("branch", "London")
    }
This also works with logical AND:
    and {
        between("balance", 500, 1000)
        eq("branch", "London")
    }
And you can also negate using logical NOT:
    not {
        between("balance", 500, 1000)
        eq("branch", "London")
    }
All top level conditions are implied to be AND'd together. #### Querying Associations Associations can be queried by having a node that matches the property name. For example say the `Account` class had many `Transaction` objects:
    class Account {
        …
        static hasMany = [transactions: Transaction]
        …
    }
We can query this association by using the property name `transactions` as a builder node:
    def c = Account.createCriteria()
    def now = new Date()
    def results = c.list {
        transactions {
            between('date', now - 10, now)
        }
    }
The above code will find all the `Account` instances that have performed `transactions` within the last 10 days. You can also nest such association queries within logical blocks:
    def c = Account.createCriteria()
    def now = new Date()
    def results = c.list {
        or {
            between('created', now - 10, now)
            transactions {
                between('date', now - 10, now)
            }
        }
    }
Here we find all accounts that have either performed transactions in the last 10 days OR have been recently created in the last 10 days. #### Querying with Projections Projections may be used to customise the results. Define a "projections" node within the criteria builder tree to use projections. There are equivalent methods within the projections node to the methods found in the Hibernate Projections class:

    def c = Account.createCriteria()def numberOfBranches = c.get {
        projections {
            countDistinct('branch')
        }
    }
When multiple fields are specified in the projection, a List of values will be returned. A single value will be returned otherwise. #### SQL Projections The criteria DSL provides access to Hibernate's SQL projection API.
    // Box is a domain class…
    class Box {
        int width
        int height
    }

    // Use SQL projections to retrieve the perimeter and area of all of the Box instances…
    def c = Box.createCriteria()def results = c.list {
        projections {
          sqlProjection '(2 * (width + height)) as perimeter, (width * height) as area', ['perimeter', 'area'], [INTEGER, INTEGER]
        }
    }
The first argument to the `sqlProjection` method is the SQL which defines the projections. The second argument is a list of Strings which represent column aliases corresponding to the projected values expressed in the SQL. The third argument is a list of `org.hibernate.type.Type` instances which correspond to the projected values expressed in the SQL. The API supports all `org.hibernate.type.Type` objects but constants like INTEGER, LONG, FLOAT etc. are provided by the DSL which correspond to all of the types defined in `org.hibernate.type.StandardBasicTypes`. Consider that the following table represents the data in the `BOX` table.
width | height
--- | ---
2 | 7
2 | 8
2 | 9
4 | 9
The query above would return results like this:
    [[18, 14], [20, 16], [22, 18], [26, 36]]
Each of the inner lists contains the 2 projected values for each `Box`, perimeter and area. Note that if there are other references in scope wherever your criteria query is expressed that have names that conflict with any of the type constants described above, the code in your criteria will refer to those references, not the type constants provided by the DSL. In the unlikely event of that happening you can disambiguate the conflict by referring to the fully qualified Hibernate type. For example `StandardBasicTypes.INTEGER` instead of `INTEGER`. If only 1 value is being projected, the alias and the type do not need to be included in a list.
    def results = c.list {
        projections {
          sqlProjection 'sum(width * height) as totalArea', 'totalArea', INTEGER
        }
    }
That query would return a single result with the value of 84 as the total area of all of the `Box` instances. The DSL supports grouped projections with the `sqlGroupProjection` method.
    def results = c.list {
        projections {
            sqlGroupProjection 'width, sum(height) as combinedHeightsForThisWidth', 'width', ['width', 'combinedHeightsForThisWidth'], [INTEGER, INTEGER]
        }
    }
The first argument to the `sqlGroupProjection` method is the SQL which defines the projections. The second argument represents the group by clause that should be part of the query. That string may be single column name or a comma separated list of column names. The third argument is a list of Strings which represent column aliases corresponding to the projected values expressed in the SQL. The fourth argument is a list of `org.hibernate.type.Type` instances which correspond to the projected values expressed in the SQL. The query above is projecting the combined heights of boxes grouped by width and would return results that look like this:
    [[2, 24], [4, 9]]
Each of the inner lists contains 2 values. The first value is a box width and the second value is the sum of the heights of all of the boxes which have that width. #### Using SQL Restrictions You can access Hibernate's SQL Restrictions capabilities.

    def c = Person.createCriteria()def peopleWithShortFirstNames = c.list {
        sqlRestriction "char_length(first_name) <= 4"
    }
SQL Restrictions may be parameterized to deal with SQL injection vulnerabilities related to dynamic restrictions.

    def c = Person.createCriteria()def peopleWithShortFirstNames = c.list {
        sqlRestriction "char_length(first_name) < ? AND char_length(first_name) > ?", [maxValue, minValue]
    }
Note that the parameter there is SQL. The `first_name` attribute referenced in the example refers to the persistence model, not the object model like in HQL queries. The `Person` property named `firstName` is mapped to the `first_name` column in the database and you must refer to that in the `sqlRestriction` string. Also note that the SQL used here is not necessarily portable across databases. #### Using Scrollable Results You can use Hibernate's ScrollableResults feature by calling the scroll method:

    def results = crit.scroll {
        maxResults(10)
    }
    def f = results.first()
    def l = results.last()
    def n = results.next()
    def p = results.previous()def future = results.scroll(10)
    def accountNumber = results.getLong('number')
To quote the documentation of Hibernate ScrollableResults: A result iterator that allows moving around within the results by arbitrary increments. The Query / ScrollableResults pattern is very similar to the JDBC PreparedStatement / ResultSet pattern and the semantics of methods of this interface are similar to the similarly named methods on ResultSet. Contrary to JDBC, columns of results are numbered from zero. #### Setting properties in the Criteria instance If a node within the builder tree doesn't match a particular criterion it will attempt to set a property on the Criteria object itself. This allows full access to all the properties in this class. This example calls `setMaxResults` and `setFirstResult` on the Criteria instance:
    import org.hibernate.FetchMode as FM
    …
    def results = c.list {
        maxResults(10)
        firstResult(50)
        fetchMode("aRelationship", FM.JOIN)
    }
#### Querying with Eager Fetching In the section on Eager and Lazy Fetching we discussed how to declaratively specify fetching to avoid the N+1 SELECT problem. However, this can also be achieved using a criteria query:
    def criteria = Task.createCriteria()
    def tasks = criteria.list{
        eq "assignee.id", task.assignee.id
        join 'assignee'
        join 'project'
        order 'priority', 'asc'
    }
Notice the usage of the `join` method: it tells the criteria API to use a `JOIN` to fetch the named associations with the `Task` instances. It's probably best not to use this for one-to-many associations though, because you will most likely end up with duplicate results. Instead, use the 'select' fetch mode:
    import org.hibernate.FetchMode as FM
    …
    def results = Airport.withCriteria {
        eq "region", "EMEA"
        fetchMode "flights", FM.SELECT
    }
Although this approach triggers a second query to get the `flights` association, you will get reliable results - even with the `maxResults` option. `fetchMode` and `join` are general settings of the query and can only be specified at the top-level, i.e. you cannot use them inside projections or association constraints. An important point to bear in mind is that if you include associations in the query constraints, those associations will automatically be eagerly loaded. For example, in this query:
    def results = Airport.withCriteria {
        eq "region", "EMEA"
        flights {
            like "number", "BA%"
        }
    }
the `flights` collection would be loaded eagerly via a join even though the fetch mode has not been explicitly set. #### Method Reference If you invoke the builder with no method name such as:
    c { … }
The build defaults to listing all the results and hence the above is equivalent to:
    c.list { … }
Method | Description
--- | ---
list | This is the default method. It returns all matching rows.
get | Returns a unique result set, i.e. just one row. The criteria has to be formed that way, that it only queries one row. This method is not to be confused with a limit to just the first row.
scroll | Returns a scrollable result set.
listDistinct | If subqueries or associations are used, one may end up with the same row multiple times in the result set, this allows listing only distinct entities and is equivalent to `DISTINCT_ROOT_ENTITY` of the CriteriaSpecification class.
count | Returns the number of matching rows.
#### Combining Criteria You can combine multiple criteria closures in the following way:

    def emeaCriteria = {
        eq "region", "EMEA"
    }def results = Airport.withCriteria {
        emeaCriteria.delegate = delegate
        emeaCriteria()
        flights {
            like "number", "BA%"
        }
    }
This technique requires that each criteria must refer to the same domain class (i.e. `Airport`). A more flexible approach is to use Detached Criteria, as described in the following section. ## 7.4.4 Detached Criteria Detached Criteria are criteria queries that are not associated with any given database session/connection. Supported since Grails 2.0, Detached Criteria queries have many uses including allowing you to create common reusable criteria queries, execute subqueries and execute batch updates/deletes. #### Building Detached Criteria Queries The primary point of entry for using the Detached Criteria is the `grails.gorm.DetachedCriteria` class which accepts a domain class as the only argument to its constructor:
    import grails.gorm.*
    …
    def criteria = new DetachedCriteria(Person)
Once you have obtained a reference to a detached criteria instance you can execute where queries or criteria queries to build up the appropriate query. To build a normal criteria query you can use the `build` method:
    def criteria = new DetachedCriteria(Person).build {
        eq 'lastName', 'Simpson'
    }
Note that methods on the `DetachedCriteria` instance do not mutate the original object but instead return a new query. In other words, you have to use the return value of the `build` method to obtain the mutated criteria object:
    def criteria = new DetachedCriteria(Person).build {
        eq 'lastName', 'Simpson'
    }
    def bartQuery = criteria.build {
        eq 'firstName', 'Bart'
    }
#### Executing Detached Criteria Queries Unlike regular criteria, Detached Criteria are lazy, in that no query is executed at the point of definition. Once a Detached Criteria query has been constructed then there are a number of useful query methods which are summarized in the table below:
Method | Description
--- | ---
list | List all matching entities
get | Return a single matching result
count | Count all matching records
exists | Return true if any matching records exist
deleteAll | Delete all matching records
updateAll(Map) | Update all matching records with the given properties
As an example the following code will list the first 4 matching records sorted by the `firstName` property:
    def criteria = new DetachedCriteria(Person).build {
        eq 'lastName', 'Simpson'
    }
    def results = criteria.list(max:4, sort:"firstName")
You can also supply additional criteria to the list method:
    def results = criteria.list(max:4, sort:"firstName") {
        gt 'age', 30
    }
To retrieve a single result you can use the `get` or `find` methods (which are synonyms):
    Person p = criteria.find() // or criteria.get()
The `DetachedCriteria` class itself also implements the `Iterable` interface which means that it can be treated like a list:
    def criteria = new DetachedCriteria(Person).build {
        eq 'lastName', 'Simpson'
    }
    criteria.each {
        println it.firstName
    }
In this case the query is only executed when the `each` method is called. The same applies to all other Groovy collection iteration methods. You can also execute dynamic finders on `DetachedCriteria` just like on domain classes. For example:
    def criteria = new DetachedCriteria(Person).build {
        eq 'lastName', 'Simpson'
    }
    def bart = criteria.findByFirstName("Bart")
#### Using Detached Criteria for Subqueries Within the context of a regular criteria query you can use `DetachedCriteria` to execute subquery. For example if you want to find all people who are older than the average age the following query will accomplish that:
    def results = Person.withCriteria {
         gt "age", new DetachedCriteria(Person).build {
             projections {
                 avg "age"
             }
         }
         order "firstName"
     }
Notice that in this case the subquery class is the same as the original criteria query class (i.e. `Person`) and hence the query can be shortened to:
    def results = Person.withCriteria {
         gt "age", {
             projections {
                 avg "age"
             }
         }
         order "firstName"
     }
If the subquery class differs from the original criteria query then you will have to use the original syntax. In the previous example the projection ensured that only a single result was returned (the average age). If your subquery returns multiple results then there are different criteria methods that need to be used to compare the result. For example to find all the people older than the ages 18 to 65 a `gtAll` query can be used:

    def results = Person.withCriteria {
        gtAll "age", {
            projections {
                property "age"
            }
            between 'age', 18, 65
        }    order "firstName"
    }
The following table summarizes criteria methods for operating on subqueries that return multiple results:
Method | Description
--- | ---
gtAll | greater than all subquery results
geAll | greater than or equal to all subquery results
ltAll | less than all subquery results
leAll | less than or equal to all subquery results
eqAll | equal to all subquery results
neAll | not equal to all subquery results
#### Batch Operations with Detached Criteria The `DetachedCriteria` class can be used to execute batch operations such as batch updates and deletes. For example, the following query will update all people with the surname "Simpson" to have the surname "Bloggs":
    def criteria = new DetachedCriteria(Person).build {
        eq 'lastName', 'Simpson'
    }
    int total = criteria.updateAll(lastName:"Bloggs")
Note that one limitation with regards to batch operations is that join queries (queries that query associations) are not allowed within the `DetachedCriteria` instance. To batch delete records you can use the `deleteAll` method:
    def criteria = new DetachedCriteria(Person).build {
        eq 'lastName', 'Simpson'
    }
    int total = criteria.deleteAll()
## 7.4.5 Hibernate Query Language (HQL) GORM classes also support Hibernate's query language HQL, a very complete reference for which can be found in the Hibernate documentation of the Hibernate documentation. GORM provides a number of methods that work with HQL including find, findAll and executeQuery. An example of a query can be seen below:
    def results =
          Book.findAll("from Book as b where b.title like 'Lord of the%'")
#### Positional and Named Parameters In this case the value passed to the query is hard coded, however you can equally use positional parameters:
    def results =
          Book.findAll("from Book as b where b.title like ?", ["The Shi%"])
    def author = Author.findByName("Stephen King")
    def books = Book.findAll("from Book as book where book.author = ?",
                             [author])
Or even named parameters:
    def results =
          Book.findAll("from Book as b " +
                       "where b.title like :search or b.author like :search",
                       [search: "The Shi%"])
    def author = Author.findByName("Stephen King")
    def books = Book.findAll("from Book as book where book.author = :author",
                             [author: author])
#### Multiline Queries - -As of Grails 3.0.3, Triple-quoted Groovy multiline Strings now work properly with HQL queries. - Use the line continuation character to separate the query across multiple lines:
    def results = Book.findAll("\
    from Book as b, \
         Author as a \
    where b.author = a and a.surname = ?", ['Smith'])
or
    def results = Book.findAll("""
    from Book as b,
         Author as a
    where b.author = a and a.surname = ?", ['Smith']
    """)
#### Pagination and Sorting You can also perform pagination and sorting whilst using HQL queries. To do so simply specify the pagination options as a Map at the end of the method call and include an "ORDER BY" clause in the HQL:
    def results =
          Book.findAll("from Book as b where " +
                       "b.title like 'Lord of the%' " +
                       "order by b.title asc",
                       [max: 10, offset: 20])
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