# Vert.x JDBC client

This client allows you to interact with any JDBC compliant database using an asynchronous API from your Vert.x application.

The client API is represented with the interface `JDBCClient`.

To use this project, add the following dependency to the dependencies section of your build descriptor:

- Maven (in your `pom.xml`):

    <dependency>
      <groupId>io.vertx</groupId>
      <artifactId>vertx-jdbc-client</artifactId>
      <version>3.4.2</version>
    </dependency>

- Gradle (in your `build.gradle` file):

    compile 'io.vertx:vertx-jdbc-client:3.4.2'

## Creating a the client

There are several ways to create a client. Let’s go through them all.

### Using default shared data source

In most cases you will want to share a data source between different client instances.

E.g. you scale your application by deploying multiple instances of your verticle and you want each verticle instance to share the same datasource so you don’t end up with multiple pools

You do this as follows:

    SQLClient client = JDBCClient.createShared(vertx, config);

The first call to `JDBCClient.createShared` will actually create the data source, and the specified config will be used.

Subsequent calls will return a new client instance that uses the same data source, so the configuration won’t be used.

### Specifying a data source name

You can create a client specifying a data source name as follows

    SQLClient client = JDBCClient.createShared(vertx, config, "MyDataSource");

If different clients are created using the same Vert.x instance and specifying the same data source name, they will share the same data source.

The first call to `JDBCClient.createShared` will actually create the data source, and the specified config will be used.

Subsequent calls will return a new client instance that uses the same data source, so the configuration won’t be used.

Use this way of creating if you wish different groups of clients to have different data sources, e.g. they’re interacting with different databases.

### Creating a client with a non shared data source

In most cases you will want to share a data source between different client instances. However, it’s possible you want to create a client instance that doesn’t share its data source with any other client.

In that case you can use `JDBCClient.createNonShared`.

    SQLClient client = JDBCClient.createNonShared(vertx, config);

This is equivalent to calling `JDBCClient.createShared` with a unique data source name each time.

### Specifying a data source

If you already have a pre-existing data source, you can also create the client directly specifying that:

    SQLClient client = JDBCClient.create(vertx, dataSource);

## Closing the client

It’s fine to keep hold of the client for a long time (e.g. the lifetime of your verticle), but once you’re done with it you should close it.

Clients that share a data source with other client instances are reference counted. Once the last one that references the same data source is closed, the data source will be closed.

### Automatic clean-up in verticles

If you’re creating clients from inside verticles, the clients will be automatically closed when the verticle is undeployed.

## Getting a connection

Once you’ve created a client you use `getConnection` to get a connection.

This will return the connection in the handler when one is ready from the pool.

    client.getConnection(res -> {
      if (res.succeeded()) {

        SQLConnection connection = res.result();

        connection.query("SELECT * FROM some_table", res2 -> {
          if (res2.succeeded()) {

            ResultSet rs = res2.result();
            // Do something with results
          }
        });
      } else {
        // Failed to get connection - deal with it
      }
    });

The connection is an instance of `SQLConnection` which is a common interface not only used by the Vert.x JDBC Client.

You can learn how to use it in the common sql interface documentation.

## Configuration

Configuration is passed to the client when creating or deploying it.

The following configuration properties generally apply:

`provider_class`

  The class name of the class actually used to manage the database connections. By default this is `io.vertx.ext.jdbc.spi.impl.C3P0DataSourceProvider` but if you want to use a different provider you can override this property and provide your implementation.

`row_stream_fetch_size`

  The size of `SQLRowStream` internal cache which used to better performance. By default it equals to `128`

Assuming the C3P0 implementation is being used (the default), the following extra configuration properties apply:

`url`

  the JDBC connection URL for the database

`driver_class`

  the class of the JDBC driver

`user`

  the username for the database

`password`

  the password for the database

`max_pool_size`

  the maximum number of connections to pool - default is `15`

`initial_pool_size`

  the number of connections to initialise the pool with - default is `3`

`min_pool_size`

  the minimum number of connections to pool

`max_statements`

  the maximum number of prepared statements to cache - default is `0`.

`max_statements_per_connection`

  the maximum number of prepared statements to cache per connection - default is `0`.

`max_idle_time`

  number of seconds after which an idle connection will be closed - default is `0` (never expire).

Other Connection Pool providers are:

- BoneCP

- Hikari

Similar to C3P0 they can be configured by passing the configuration values on the JSON config object. For the special case where you do not want to deploy your app as a fat jar but run with a vert.x distribution, then it is recommented to use BoneCP if you have no write permissions to add the JDBC driver to the vert.x lib directory and are passing it using the `-cp` command line flag.

If you want to configure any other C3P0 properties, you can add a file `c3p0.properties` to the classpath.

Here’s an example of configuring a service:

    JsonObject config = new JsonObject()
      .put("url", "jdbc:hsqldb:mem:test?shutdown=true")
      .put("driver_class", "org.hsqldb.jdbcDriver")
      .put("max_pool_size", 30);

    SQLClient client = JDBCClient.createShared(vertx, config);

Hikari uses a different set of properties:

- `jdbcUrl` for the JDBC URL

- `driverClassName` for the JDBC driven class name

- `maximumPoolSize` for the pool size

- `username` for the login (`password` for the password)

Refer to the Hikari documentation for further details. Also refer to the BoneCP documentation to configure BoneCP.

## JDBC Drivers

If you are using the default `DataSourceProvider` (relying on c3p0), you would need to copy the JDBC driver class in your classpath.

If your application is packaged as a fat jar, be sure to embed the jdbc driver. If your application is launched with the `vertx` command line, copy the JDBC driver to `${VERTX_HOME}/lib`.

The behavior may be different when using a different connection pool.

## Data types

Due to the fact that Vert.x uses JSON as its standard message format there will be many limitations to the data types accepted by the client. You will get out of the box the standard:

- null

- boolean

- number

- string

There is also an optimistic cast for temporal types (TIME, DATE, TIMESTAMP) and optionally disabled for UUID. UUIDs are supported by many databases but not all. For example MySQL does not support it so the recommended way is to use a VARCHAR(36) column. For other engines UUID optimistic casting can be enabled using the client config json as:

    { "castUUID": true }

When this config is present UUIDs will be handled as a native type.

## Use as OSGi bundle

Vert.x JDBC client can be used as an OSGi bundle. However notice that you would need to deploy all dependencies first. Some connection pool requires the JDBC driver to be loaded from the classpath, and so cannot be packaged / deployed as bundle.