Apache DdlUtils入门

Introduction 

DdlUtils is a small, easy-to-use component for working with Database Definition (DDL) files. These are XML files that contain the definition of a database schema, e.g. tables and columns. These files can be fed into DdlUtils via its Ant task or programmatically in order to create the corresponding database or alter it so that it corresponds to the DDL. Likewise, DdlUtils can generate a DDL file for an existing database.

DdlUtils既可以根据定义数据库schema的XML文件（DDL文件）创建或者修改数据库，也可以为现有的数据库生成一个DDL文件。

简单来讲，DdlUtils既是一个library，也是操作数据库schema的Ant tasks。它可以创建和删除数据库，创建、修改和删除表。此外，还可以将XML中定义的数据插入数据库，或者将数据库中的数据读到XML文件中。

DdlUtils追求数据库独立性。schema文件是Turbine XML格式。这种XML格式文件同样用在 Torque 和 OJB 中。

DdlUtils APIs

DdlUtils的核心是定义在org.apache.ddlutils.model中的数据库model，它由表示数据库的schema的各种类组成。

Reading from XML

import org.apache.ddlutils.io.DatabaseIO;
import org.apache.ddlutils.model.Database;

...

public Database readDatabaseFromXML(String fileName)
{
    return new DatabaseIO().read(fileName);
}

Writing to XML

import org.apache.ddlutils.io.DatabaseIO;
import org.apache.ddlutils.model.Database;

...

public void writeDatabaseToXML(Database db, String fileName)
{
    new DatabaseIO().write(db, fileName);
}

Reading the model from a live database

import javax.sql.DataSource;
import org.apache.ddlutils.Platform;
import org.apache.ddlutils.PlatformFactory;
import org.apache.ddlutils.model.Database;

...

public Database readDatabase(DataSource dataSource)
{
    Platform platform = PlatformFactory.createNewPlatformInstance(dataSource);

    return platform.readModelFromDatabase("model");
}

Changing a database

修改数据库有两种方式：将数据库重置为model定义样子；修改数据库为model定义的样子。可以理解成对数据库schema的修改。

import javax.sql.DataSource;
import org.apache.ddlutils.Platform;
import org.apache.ddlutils.PlatformFactory;
import org.apache.ddlutils.model.Database;

...

public void changeDatabase(DataSource dataSource,
                           Database   targetModel,
                           boolean    alterDb)
{
    Platform platform = PlatformFactory.createNewPlatformInstance(dataSource);

    if (alterDb)
    {
        platform.alterTables(targetModel, false);
    }
    else
    {
        platform.createTables(targetModel, true, false);
    }
}

Inserting data into database

DdlUtils使用 DynaBeans 插入数据。对于数据库model定义的每个table，a so-called dyna class is created that represents the table with its columns.

import javax.sql.DataSource;
import org.apache.commons.beanutils.DynaBean;
import org.apache.ddlutils.Platform;
import org.apache.ddlutils.PlatformFactory;
import org.apache.ddlutils.model.Database;

...

public void insertData(DataSource dataSource,
                       Database   database)
{
    Platform platform = PlatformFactory.createNewPlatformInstance(dataSource);

    // "author" is a table of the model
    DynaBean author = database.createDynaBeanFor("author", false);

    // "name" and "whatever" are columns of table "author"
    author.set("name",     "James");
    author.set("whatever", new Integer(1234));

    platform.insert(database, author);
}

Getting data from a database

同插数据一样，DdlUtils使用 dyna beans 来获取数据库放回的数据。

import java.util.ArrayList;
import java.util.Iterator;
import javax.sql.DataSource;
import org.apache.commons.beanutils.DynaBean;
import org.apache.ddlutils.Platform;
import org.apache.ddlutils.PlatformFactory;
import org.apache.ddlutils.model.Database;
import org.apache.ddlutils.model.Table;

...

public void dumpBooks(DataSource dataSource,
                      Database   database)
{
    Platform  platform = PlatformFactory.createNewPlatformInstance(dataSource);
    ArrayList params   = new ArrayList();

    params.add("Some title");

    Iterator it = platform.query(database,
                                 "select * from book where title = ?",
                                 params,
                                 new Table[] { database.findTable("book") });

    while (it.hasNext())
    {
        DynaBean book = (DynaBean)it.next();

        System.out.println(book.get("title"));
    }
}

Note: 以上只是样例APIs，仅供参考。

Reference

https://db.apache.org/ddlutils/api-usage.html

https://db.apache.org/ddlutils/databases/mysql.html