Add the following dependencies to your Maven project:

<dependency>
  <groupId>com.querydsl</groupId>
  <artifactId>querydsl-sql</artifactId>
  <version>${querydsl.version}</version>
</dependency>

<dependency>
  <groupId>com.querydsl</groupId>
  <artifactId>querydsl-sql-codegen</artifactId>
  <version>${querydsl.version}</version>
  <scope>provided</scope>
</dependency>

The querydsl-sql-codegen dependency can be skipped, if code generation happens via Maven.

This functionality should be primarily used via the Maven plugin. Here is an example:

<project>
  <build>
    <plugins>
      ...
      <plugin>
        <groupId>com.querydsl</groupId>
        <artifactId>querydsl-maven-plugin</artifactId>
        <version>${querydsl.version}</version>
        <executions>
          <execution>
            <goals>
              <goal>export</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <jdbcDriver>org.apache.derby.jdbc.EmbeddedDriver</jdbcDriver>
          <jdbcUrl>jdbc:derby:target/demoDB;create=true</jdbcUrl>
          <packageName>com.myproject.domain</packageName>
          <targetFolder>${project.basedir}/target/generated-sources/java</targetFolder>
        </configuration>
        <dependencies>
          <dependency>
            <groupId>org.apache.derby</groupId>
            <artifactId>derby</artifactId>
            <version>${derby.version}</version>
          </dependency>
        </dependencies>
      </plugin>
      ...
    </plugins>
  </build>
</project>

Use the goal test-export to treat the target folder as a test source folder for use with test code.

Custom types can be used to register additional Type implementations:

<customTypes>
  <customType>com.querydsl.sql.types.InputStreamType</customType>
</customTypes>

Type mappings can be used to register table.column specific java types:

<typeMappings>
  <typeMapping>
    <table>IMAGE</table>
    <column>CONTENTS</column>
    <type>java.io.InputStream</type>
  </typeMapping>
</typeMappings>

The defaults for the numeric mappings are

They can be customized for specific total/decimal digits combinations like this:

<numericMappings>
  <numericMapping>
    <total>1</total>
    <decimal>0</decimal>
    <javaType>java.lang.Byte</javaType>
  </numericMapping>
</numericMappings>

Imports can be used to add cross-schema foreign keys support.

Schemas, tables and columns can also be renamed using the plugin. Here are some examples:

Renaming a schema:

<renameMappings>
  <renameMapping>
    <fromSchema>PROD</fromSchema>
    <toSchema>TEST</toSchema>
  </renameMapping>
</renameMappings>

Renaming a table:

<renameMappings>
  <renameMapping>
    <fromSchema>PROD</fromSchema>
    <fromTable>CUSTOMER</fromTable>
    <toTable>CSTMR</toTable>
  </renameMapping>
</renameMappings>

Renaming a column:

<renameMappings>
  <renameMapping>
    <fromSchema>PROD</fromSchema>
    <fromTable>CUSTOMER</fromTable>
    <fromColumn>ID</fromColumn>
    <toColumn>IDX</toTable>
  </renameMapping>
</renameMappings>

Note: fromSchema can be omitted when renaming tables and columns.

Compared to APT based code generation certain functionality is not available such as QueryDelegate annotation handling.

The ANT task com.querydsl.sql.codegen.ant.AntMetaDataExporter of the querydsl-sql module provides the same functionality as an ANT task. The configuration parameters of the task are the same as for the Maven plugin, except for the composite types.

The composite types are used without the wrapper element like in this example.

<project name="testproject" default="codegen" basedir=".">

  <taskdef name="codegen" classname="com.querydsl.sql.codegen.ant.AntMetaDataExporter"/>

  <target name="codegen">
    <codegen
      jdbcDriver="org.h2.Driver"
      jdbcUser="sa"
      jdbcUrl="jdbc:h2:/dbs/db1"
      packageName="test"
      targetFolder="target/generated-sources/java">
      <renameMapping fromSchema="PUBLIC" toSchema="PUB"/>
    </codegen>
  </target>
</project>

To get started export your schema into Querydsl query types like this:

java.sql.Connection conn = ...;
MetaDataExporter exporter = new MetaDataExporter();
exporter.setPackageName("com.myproject.mydomain");
exporter.setTargetFolder(new File("target/generated-sources/java"));
exporter.export(conn.getMetaData());

This declares that the database schema is to be mirrored into the com.myproject.domain package in the target/generated-sources/java folder.

The generated types have the table name transformed to mixed case as the class name and a similar mixed case transformation applied to the columns which are available as property paths in the query type.

In addition to this primary key and foreign key constraints are provided as fields which can be used for compact join declarations.

The configuration is done via the com.querydsl.sql.Configuration class which takes the Querydsl SQL dialect as an argument. For H2 you would create it like this

SQLTemplates templates = new H2Templates();
Configuration configuration = new Configuration(templates);

Querydsl uses SQL dialects to customize the SQL serialization needed for different relational databases. The available dialects are:

For customized SQLTemplates instances you can use the builder pattern like this

  H2Templates.builder()
     .printSchema() // to include the schema in the output
     .quote()       // to quote names
     .newLineToSingleSpace() // to replace new lines with single space in the output
     .escape(ch)    // to set the escape char
     .build();      // to get the customized SQLTemplates instance

The methods of the Configuration class can be used to enable direct serialization of literals via setUseLiterals(true), override schema and tables and register custom types. For full details look at the javadocs of Configuration.

For the following examples we will be using the SQLQueryFactory class for query creation. Using it results in more concise code compared to constructor based query creation.

SQLQueryFactory queryFactory = new SQLQueryFactory(configuration, dataSource);

Querying with Querydsl SQL is as simple as this:

QCustomer customer = new QCustomer("c");

List<String> lastNames = queryFactory.select(customer.lastName).from(customer)
    .where(customer.firstName.eq("Bob"))
    .fetch();

which is transformed into the following sql query, assuming that the related table name is customer and the columns first_name and last_name:

SELECT c.last_name
FROM customer c
WHERE c.first_name = 'Bob'

Use the the cascading methods of the SQLQuery class like this

select: Set the projection of the query. (Not necessary if created via query factory)

from: Add the query sources here.

innerJoin, join, leftJoin, rightJoin, fullJoin, on: Add join elements using these constructs. For the join methods the first argument is the join source and the second the target (alias).

where: Add query filters, either in varargs form separated via commas or cascaded via the and-operator.

groupBy: Add group by arguments in varargs form.

having: Add having filter of the "group by" grouping as an varags array of Predicate expressions.

orderBy: Add ordering of the result as an varargs array of order expressions. Use asc() and desc() on numeric, string and other comparable expression to access the OrderSpecifier instances.

limit, offset, restrict: Set the paging of the result. Limit for max results, offset for skipping rows and restrict for defining both in one call.

Joins are constructed using the following syntax:

QCustomer customer = QCustomer.customer;
QCompany company = QCompany.company;
queryFactory.select(customer.firstName, customer.lastName, company.name)
    .from(customer)
    .innerJoin(customer.company, company)
    .fetch();

and for a left join:

queryFactory.select(customer.firstName, customer.lastName, company.name)
    .from(customer)
    .leftJoin(customer.company, company)
    .fetch();

Alternatively the join condition can also be written out:

queryFactory.select(customer.firstName, customer.lastName, company.name)
    .from(customer)
    .leftJoin(company).on(customer.company.eq(company))
    .fetch();

The syntax for declaring ordering is

queryFactory.select(customer.firstName, customer.lastName)
    .from(customer)
    .orderBy(customer.lastName.asc(), customer.firstName.asc())
    .fetch();

which is equivalent to the following native SQL

SELECT c.first_name, c.last_name
FROM customer c
ORDER BY c.last_name ASC, c.first_name ASC

Grouping can be done in the following form

queryFactory.select(customer.lastName)
    .from(customer)
    .groupBy(customer.lastName)
    .fetch();

which is equivalent to the following native SQL

SELECT c.last_name
FROM customer c
GROUP BY c.last_name

To create a subquery you can use one of the factory methods of SQLExpressions and add the query parameters via from, where etc.

QCustomer customer = QCustomer.customer;
QCustomer customer2 = new QCustomer("customer2");
queryFactory.select(customer.all())
    .from(customer)
    .where(customer.status.eq(
        SQLExpressions.select(customer2.status.max()).from(customer2)))
    .fetch()

Another example

QStatus status = QStatus.status;
queryFactory.select(customer.all())
    .from(customer)
    .where(customer.status.in(
        SQLExpressions.select(status.id).from(status).where(status.level.lt(3))))
    .fetch();

To select literals you need to create constant instances for them like this:

queryFactory.select(Expressions.constant(1),
                    Expressions.constant("abc"));

The class com.querydsl.core.types.dsl.Expressions offers also other useful static methods for projections, operation and template creation.

Custom query extensions to support engine specific syntax can be created by subclassing AbstractSQLQuery and adding flagging methods like in the given MySQLQuery example:

public class MySQLQuery<T> extends AbstractSQLQuery<T, MySQLQuery<T>> {

    public MySQLQuery(Connection conn) {
        this(conn, new MySQLTemplates(), new DefaultQueryMetadata());
    }

    public MySQLQuery(Connection conn, SQLTemplates templates) {
        this(conn, templates, new DefaultQueryMetadata());
    }

    protected MySQLQuery(Connection conn, SQLTemplates templates, QueryMetadata metadata) {
        super(conn, new Configuration(templates), metadata);
    }

    public MySQLQuery bigResult() {
        return addFlag(Position.AFTER_SELECT, "SQL_BIG_RESULT ");
    }

    public MySQLQuery bufferResult() {
        return addFlag(Position.AFTER_SELECT, "SQL_BUFFER_RESULT ");
    }


    // ...
}

The flags are custom SQL snippets that can be inserted at specific points in the serialization. The supported positions are the enums of the com.querydsl.core.QueryFlag.Position enum class.

Window functions are supported in Querydsl via the methods in the SQLExpressions class.

Usage example:

queryFactory.select(SQLExpressions.rowNumber()
        .over()
        .partitionBy(employee.name)
        .orderBy(employee.id))
     .from(employee)

Common table expressions are supported in Querydsl SQL via two syntax variants

QEmployee employee = QEmployee.employee;
queryFactory.with(employee, SQLExpressions.select(employee.all)
                                          .from(employee)
                                          .where(employee.name.startsWith("A")))
            .from(...)

And using a column listing

QEmployee employee = QEmployee.employee;
queryFactory.with(employee, employee.id, employee.name)
            .as(SQLExpressions.select(employee.id, employee.name)
                              .from(employee)
                              .where(employee.name.startsWith("A")))
            .from(...)

If the columns of the common table expression are a subset of an existing table or view it is advisable to use a generated path type for it, e.g. QEmployee in this case, but if the columns don't fit any existing table PathBuilder can be used instead.

Below is an example for such a case

QEmployee employee = QEmployee.employee;
QDepartment department = QDepartment.department;
PathBuilder<Tuple> emp = new PathBuilder<Tuple>(Tuple.class, "emp");
queryFactory.with(emp, SQLExpressions.select(employee.id, employee.name, employee.departmentId,
                                          department.name.as("departmentName"))
                                      .from(employee)
                                      .innerJoin(department).on(employee.departmentId.eq(department.id))))
            .from(...)

Other SQL expressions are also available from the SQLExpressions class as static methods.

Querydsl SQL supports usage of JDBC batch updates through the DML APIs. If you have consecutive DML calls with a similar structure, you can bundle the the calls via addBatch() usage into one DMLClause. See the examples how it works for UPDATE, DELETE and INSERT.

Update:

QSurvey survey = QSurvey.survey;

queryFactory.insert(survey).values(2, "A").execute();
queryFactory.insert(survey).values(3, "B").execute();

SQLUpdateClause update = queryFactory.update(survey);
update.set(survey.name, "AA").where(survey.name.eq("A")).addBatch();
update.set(survey.name, "BB").where(survey.name.eq("B")).addBatch();

Delete:

queryFactory.insert(survey).values(2, "A").execute();
queryFactory.insert(survey).values(3, "B").execute();

SQLDeleteClause delete = queryFactory.delete(survey);
delete.where(survey.name.eq("A")).addBatch();
delete.where(survey.name.eq("B")).addBatch();
assertEquals(2, delete.execute());

Insert:

SQLInsertClause insert = queryFactory.insert(survey);
insert.set(survey.id, 5).set(survey.name, "5").addBatch();
insert.set(survey.id, 6).set(survey.name, "6").addBatch();
assertEquals(2, insert.execute());

To create JavaBean DTO types for the tables of your schema use the MetaDataExporter like this:

java.sql.Connection conn = ...;
MetaDataExporter exporter = new MetaDataExporter();
exporter.setPackageName("com.myproject.mydomain");
exporter.setTargetFolder(new File("src/main/java"));
exporter.setBeanSerializer(new BeanSerializer());
exporter.export(conn.getMetaData());

Now you can use the bean types as arguments to the populate method in DML clauses and you can project directly to bean types in queries. Here is a simple example in JUnit form:

QEmployee e = new QEmployee("e");

// Insert
Employee employee = new Employee();
employee.setFirstname("John");
Integer id = queryFactory.insert(e).populate(employee).executeWithKey(e.id);
employee.setId(id);

// Update
employee.setLastname("Smith");
assertEquals(1l, queryFactory.update(e).populate(employee).where(e.id.eq(employee.getId())).execute());

// Query
Employee smith = queryFactory.selectFrom(e).where(e.lastname.eq("Smith")).fetchOne();
assertEquals("John", smith.getFirstname());

// Delete
assertEquals(1l, queryFactory.delete(e).where(e.id.eq(employee.getId())).execute());

The SQL query and bindings can be extracted via the getSQL method:

SQLBindings bindings = query.getSQL();
System.out.println(bindings.getSQL());

If you need also all literals in the SQL string you can enable literal serialization on the query or configuration level via setUseLiterals(true).

Querydsl SQL provides the possibility to declare custom type mappings for ResultSet/Statement interaction. The custom type mappings can be declared in com.querydsl.sql.Configuration instances, which are supplied as constructor arguments to the actual queries:

Configuration configuration = new Configuration(new H2Templates());
// overrides the mapping for Types.DATE
configuration.register(new UtilDateType());

And for a table column

Configuration configuration = new Configuration(new H2Templates());
// declares a mapping for the gender column in the person table
configuration.register("person", "gender",  new EnumByNameType<Gender>(Gender.class));

To customize a numeric mapping you can use the registerNumeric method like this

configuration.registerNumeric(5,2,Float.class);

This will map the Float type to the NUMERIC(5,2) type.

SQLListener is a listener interface that can be used to listen to queries and DML clause. SQLListener instances can be registered either on the configuration and on the query/clause level via the addListener method.

Use cases for listeners are data synchronization, logging, caching and validation.

Querydsl SQL integrates with Spring through the querydsl-sql-spring module:

<dependency>
  <groupId>com.querydsl</groupId>
  <artifactId>querydsl-sql-spring</artifactId>
  <version>${querydsl.version}</version>
</dependency>

It provides Spring exception translation and a Spring connection provider for usage of Querydsl SQL with Spring transaction managers. Below is a configuration example:

package com.querydsl.example.config;

import com.querydsl.sql.H2Templates;
import com.querydsl.sql.SQLQueryFactory;
import com.querydsl.sql.SQLTemplates;
import com.querydsl.sql.spring.SpringConnectionProvider;
import com.querydsl.sql.spring.SpringExceptionTranslator;
import com.querydsl.sql.types.DateTimeType;
import com.querydsl.sql.types.LocalDateType;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.core.env.Environment;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;
import org.springframework.transaction.PlatformTransactionManager;

import javax.sql.DataSource;
import java.sql.Connection;

@Configuration
public class JdbcConfiguration {

    @Bean
    public DataSource dataSource() {
        // implementation omitted
    }

    @Bean
    public PlatformTransactionManager transactionManager() {
        return new DataSourceTransactionManager(dataSource());
    }

    @Bean
    public com.querydsl.sql.Configuration querydslConfiguration() {
        SQLTemplates templates = H2Templates.builder().build(); //change to your Templates
        com.querydsl.sql.Configuration configuration = new com.querydsl.sql.Configuration(templates);
        configuration.setExceptionTranslator(new SpringExceptionTranslator());
        return configuration;
    }

    @Bean
    public SQLQueryFactory queryFactory() {
        SpringConnectionProvider provider = new SpringConnectionProvider(dataSource());
        return new SQLQueryFactory(querydslConfiguration(), provider);
    }

}