Generic support for Querydsl usage in Scala is available via querydsl-scala module. To add it to your Maven build, use the following snippet :
<dependency> <groupId>com.mysema.querydsl</groupId> <artifactId>querydsl-scala</artifactId> <version>${querydsl.version}</version> </dependency>
Querydsl for Scala provides an alternative DSL for expression construction. The Scala DSL utilizes language features such as operator overloading, function pointers and implicit imports for enhanced readability and conciseness.
Here is an overview of the main alternatives :
//Standard Alternative expr isNotNull expr is not(null) expr isNull expr is null expr eq "Ben" expr === "Ben" expr ne "Ben" expr !== "Ben" expr append "X" expr + "X" expr isEmpty expr is empty expr isNotEmpoty expr not empty // boolean left and right left && right left or right left || right expr not !expr // comparison expr lt 5 expr < 5 expr loe 5 expr <= 5 expr gt 5 expr > 5 expr goe 5 expr >= 5 expr notBetween(2,6) expr not between (2,6) expr negate -expr // numeric expr add 3 expr + 3 expr subtract 3 expr - 3 expr divide 3 expr / 3 expr multiply 3 expr * 3 expr mod 5 expr % 5 // collection list.get(0) list(0) map.get("X") map("X")
The Querydsl Scala module offers a few implicit conversion to make Querydsl query projections more Scala compatible.
The RichProjectable
and RichSimpleProjectable
wrappers should be used to enable
Scala projections for Querydsl queries.
By importing the contents of com.mysema.query.scala.Helpers
the needed implicit conversions become available.
For example the following query with the standard API would return a java.util.List
of
type Object[]
.
query.from(person).list(person.firstName, person.lastName, person.age)
With the added conversions you can use select instead of list for Scala list typed results, unique instead of uniqueResult for Option typed results and single instead of singleResult for Option typed results.
The previous query could be expressed like this with the implicit conversions:
import com.mysema.query.scala.Helpers._
query.from(person).select(person.firstName, person.lastName, person.age)
In this case the result type would be List[(String,String,Integer)] or in other words List of Tuple3[String,String,Integer].
Like with Querydsl SQL for Java you need to generate Query types to be able to construct your queries. The following code examples show how this is done :
Generation without Bean types :
val directory = new java.io.File("target/jdbcgen1") val namingStrategy = new DefaultNamingStrategy() val exporter = new MetaDataExporter() exporter.setNamePrefix("Q") exporter.setPackageName("com.mysema") exporter.setSchemaPattern("PUBLIC") exporter.setTargetFolder(directory) exporter.setSerializerClass(classOf[ScalaMetaDataSerializer]) exporter.setCreateScalaSources(true) exporter.setTypeMappings(ScalaTypeMappings.create) exporter.export(connection.getMetaData)
Generation with Bean types :
val directory = new java.io.File("target/jdbcgen2") val namingStrategy = new DefaultNamingStrategy() val exporter = new MetaDataExporter() exporter.setNamePrefix("Q") exporter.setPackageName("com.mysema") exporter.setSchemaPattern("PUBLIC") exporter.setTargetFolder(directory) exporter.setSerializerClass(classOf[ScalaMetaDataSerializer]) exporter.setBeanSerializerClass(classOf[ScalaBeanSerializer]) exporter.setCreateScalaSources(true) exporter.setTypeMappings(ScalaTypeMappings.create) exporter.export(connection.getMetaData)
Querydsl Scala provides a compact query syntax for Querydsl SQL. The syntax is inspired by domain oriented query syntaxes like that from the Rogue framework.
The domain oriented queries are implemented as implicit conversions from
RelationalPath
instances into queries. This functionality
can be made available by implementing the
com.mysema.query.scala.sql.SQLHelpers
trait in your service or DAO classes.
Using this compact syntax you can use your meta model classes as a starting point for queries.
Instead of the following normal syntax
query().from(employee).select(employee.firstName, employee.lastName)
you could use the companion object of Employee or QEmployee and write it like this
Employee.select(_.firstName, _.lastName)
Instead of giving expressions to orderBy, where, select, single and unique you can give functions which take the root expression of the query and return another expression. The expanded form of the previous example would be
Employee.select({ e => e.firstName }, { e => e.lastName })
See the signature of the com.mysema.query.scala.sql.RichSimpleQuery
class for details.
Scala sources for SQL metatypes and projections can be generated with querydsl-maven-plugin. Here is an example configuration
<plugin> <groupId>com.mysema.querydsl</groupId> <artifactId>querydsl-maven-plugin</artifactId> <version>${querydsl.version}</version> <configuration> <jdbcDriver>com.mysql.jdbc.Driver</jdbcDriver> <jdbcUrl>jdbc:mysql://localhost:3306/test</jdbcUrl> <jdbcUser>matko</jdbcUser> <jdbcPassword>matko</jdbcPassword> <packageName>com.example.schema</packageName> <targetFolder>${project.basedir}/src/main/scala</targetFolder> <exportBeans>true</exportBeans> <createScalaSources>true</createScalaSources> </configuration> <dependencies> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.16</version> </dependency> <dependency> <groupId>com.mysema.querydsl</groupId> <artifactId>querydsl-scala</artifactId> <version>${querydsl.version}</version> </dependency> <dependency> <groupId>org.scala-lang</groupId> <artifactId>scala-library</artifactId> <version>${scala.version}</version> </dependency> </dependencies> </plugin>
The maven goal to execute is querydsl:export.
When querying with other backends the Expression model has to be created manually or alternatively the alias functionality can be used.
Here is a minimal example with JPA :
@Entity class User { @BeanProperty @Id var id: Integer = _; @BeanProperty var userName: String = _; @BeanProperty @ManyToOne var department: Department = _; } @Entity class Department { @BeanProperty @Id var id: Integer = _; @BeanProperty var name: String = _; }
And here are some query examples
List
val person = Person as "person" query.from(person).where(person.firstName like "Rob%").list(person)
Unique result
query.from(person).where(person.firstName like "Rob%").unique(person)
Long where
query.from(person) .where(person.firstName like "Rob%", person.lastName like "An%") .list(person)
Order
query.from(person).orderBy(person.firstName asc).list(person)
Not null
query.from(person) .where(person.firstName isEmpty, person.lastName isNotNull) .list(person)
The factory method for query creation is
def query() = new JPAQuery(entityManager)
In addition to queries you need variables which can be created like this
val person = Person as "person"
Note: the Scala support is not yet available if you use Hibernate with an XML based configuration. HibernateDomainExporter currently only outputs Java source files.