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[[library-sql,SQL Library]]
= SQL =

[devstatus]
--------------
source=libraries/sql/dev-status.xml
--------------


The SQL Library provides facilities for working with SQL databases.

The center piece is the DataSource support that comes with
<<library-circuitbreaker>> and <<library-jmx>> support.

Moreover, supplementary libraries helps dealing with different connection pool implementations and schema migrations.
None of theses libraries depends on an actual JDBC driver, you are free to use the one that suits your needs.

include::../../build/docs/buildinfo/artifact.txt[]


== DataSource and connection pools ==

DataSource support comes in three flavors:

- using the http://jolbox.com/[BoneCP] connection pool
- using the http://commons.apache.org/dbcp/[Apache DBCP] connection pool
- importing an existing DataSource provided at assembly time


=== Connection Pools ===

Connection Pools support is provided by supplementary libraries.

*BoneCP*

[devstatus]
--------------
source=libraries/sql-bonecp/dev-status.xml
--------------

include::../../../sql-bonecp/build/docs/buildinfo/artifact.txt[]

BoneCP support resides in the *sql-bonecp* module.

[snippet,java]
----
source=libraries/sql/src/test/java/org/apache/polygene/library/sql/DocumentationSupport.java
tag=bonecp
----

*Apache DBCP*

[devstatus]
--------------
source=libraries/sql-dbcp/dev-status.xml
--------------

include::../../../sql-dbcp/build/docs/buildinfo/artifact.txt[]

[snippet,java]
----
source=libraries/sql/src/test/java/org/apache/polygene/library/sql/DocumentationSupport.java
tag=dbcp
----


=== DataSource ===

*Assembly*

[snippet,java]
----
source=libraries/sql/src/test/java/org/apache/polygene/library/sql/DocumentationSupport.java
tag=datasource
----

Assembled DataSources must be visible from the connection pool importer service.

*Configuration*

You need to provide a DataSource Configuration Entity per assembled DataSource.
See <<howto-configure-service>>.

[snippet,java]
----
source=libraries/sql/src/main/java/org/apache/polygene/library/sql/datasource/DataSourceConfigurationState.java
tag=config
----

Sample DataSource configuration defaults:

[source]
----
include::../test/resources/testds.properties[]
----


=== Importing an existing DataSource ===

Importing an existing DataSource at assembly time is usefull when your Polygene
Application runs in an environment where DataSource are already provided.

[snippet,java]
----
source=libraries/sql/src/test/java/org/apache/polygene/library/sql/datasource/ExternalDataSourceTest.java
tag=assembly
----

This mechanism is provided as an integration convenience and using the embedded
connection pools described above is recommended.


== Circuit Breaker ==

Assemblers for managed and external DataSource takes an optional
CircuitBreaker and set it as <<def-metainfo>> of the DataSource.

[snippet,java]
----
source=libraries/sql/src/test/java/org/apache/polygene/library/sql/DocumentationSupport.java
tag=cb-assembly
----

Then, when you gets injected or lookup a DataSource it will be automatically wrapped
by a CircuitBreaker proxy.

[snippet,java]
----
source=libraries/sql/src/test/java/org/apache/polygene/library/sql/DocumentationSupport.java
tag=cb-datasource
----


== JMX ==

Thanks to the <<library-jmx>> the Configuration of DataSources is exposed
through JMX.

[snippet,java]
----
source=libraries/sql/src/test/java/org/apache/polygene/library/sql/jmx/DataSourceConfigurationManagerServiceTest.java
tag=jmx
----

Every DataSource visible from the DataSourceConfigurationManager Service
will get its Configuration available using a JMX client.

Note that the JMX support does not apply to existing DataSource imported as
described above.


== Schema migration ==

Database schema migration can be delegated to http://www.liquibase.org/[Liquibase].

[devstatus]
--------------
source=libraries/sql-liquibase/dev-status.xml
--------------

include::../../../sql-liquibase/build/docs/buildinfo/artifact.txt[]

*Assembly*

[snippet,java]
----
source=libraries/sql-liquibase/src/test/java/org/apache/polygene/library/sql/liquibase/LiquibaseServiceTest.java
tag=assembly
----

The LiquibaseService is activated on Application startup and if enabled it
applies the configured changelog.

*Configuration*

[snippet,java]
----
source=libraries/sql-liquibase/src/main/java/org/apache/polygene/library/sql/liquibase/LiquibaseConfiguration.java
tag=config
----

For the Liquibase service to be enabled you must set it's Configuration
+enabled+ Property to TRUE. *contexts* and *changeLog* are optional.