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)        

    
query().from(employee).select(employee.firstName, employee.lastName)        

    
Employee.select(_.firstName, _.lastName)        

    
Employee.select({ e => e.firstName }, { e => e.lastName })        

      
<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>     

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/Hibernate :

  
@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 main import for Querydsl Scala integration is the following

import com.mysema.query.scala.Conversions._

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"