activiti兼容达梦数据库

前言

由于达梦兼容oracle，因此兼容达梦数据库，本质上就是让应用识别到是达梦数据库后，将它当作oracle对待即可，本文中activiti版本为5.X

定义数据库类型枚举

public enum MyDbConfig {
    /**
     * 达梦数据库（兼容oracle）
     */
    DM("dm", "DM DBMS", "oracle");
    /**
     * 数据库类型名称
     */
    private String dbTypeName;
    /**
     * 数据库产品名称
     */
    private String dbProductName;
    /**
     * 兼容数据库类型名称
     */
    private String compatibleDbTypeName;

    public String getDbProductName() {
        return dbProductName;
    }

    public String getDbTypeName() {
        return dbTypeName;
    }

    public String getCompatibleDbTypeName() {
        return compatibleDbTypeName;
    }

    MyDbConfig(String dbTypeName, String dbProductName, String compatibleDbTypeName) {
        this.dbTypeName = dbTypeName;
        this.dbProductName = dbProductName;
        this.compatibleDbTypeName = compatibleDbTypeName;
    }
}

初始化达梦配置类

import org.activiti.engine.impl.db.DbSqlSessionFactory;

import java.util.Properties;

public class InitDmConfig {
    /**
     * 初始化达梦数据库配置（因其声称兼容oracle，故参照oracle的配置来加）
     * 

     * org.activiti.engine.impl.cfg.ProcessEngineConfigurationImpl#databaseTypeMappings
     * ProcessEngineConfigurationImpl#getDefaultDatabaseTypeMappings()
     * 
     *
     * @param databaseTypeMappings 数据库类型映射
     * @see org.activiti.engine.impl.cfg.ProcessEngineConfigurationImpl
     * @see org.activiti.engine.impl.db.DbSqlSessionFactory
     */
    public static void init(Properties databaseTypeMappings) {
        MyDbConfig value = MyDbConfig.DM;
        databaseTypeMappings.setProperty(value.getDbProductName(), value.getDbTypeName());

        DbSqlSessionFactory.databaseSpecificLimitBeforeStatements.put(value.getDbTypeName(),
                DbSqlSessionFactory.databaseSpecificLimitBeforeStatements.get(value.getCompatibleDbTypeName()));

        DbSqlSessionFactory.databaseSpecificLimitAfterStatements.put(value.getDbTypeName(),
                DbSqlSessionFactory.databaseSpecificLimitAfterStatements.get(value.getCompatibleDbTypeName()));

        DbSqlSessionFactory.databaseSpecificLimitBetweenStatements.put(value.getDbTypeName(),
                DbSqlSessionFactory.databaseSpecificLimitBetweenStatements.get(value.getCompatibleDbTypeName()));

        DbSqlSessionFactory.databaseSpecificOrderByStatements.put(value.getDbTypeName(),
                DbSqlSessionFactory.databaseSpecificOrderByStatements.get(value.getCompatibleDbTypeName()));

        DbSqlSessionFactory.databaseOuterJoinLimitBetweenStatements.put(value.getDbTypeName(),
                DbSqlSessionFactory.databaseOuterJoinLimitBetweenStatements.get(value.getCompatibleDbTypeName()));
    }
}

注意，上文类的参数databaseTypeMappings与org.activiti.engine.impl.cfg.ProcessEngineConfigurationImpl#getDefaultDatabaseTypeMappings()的返回值对应，即类ProcessEngineConfigurationImpl的databaseTypeMappings属性，目的就是向该配置中添加达梦相关配置

调用达梦初始化配置类

activiti提供了抽象类ProcessEngineConfigurationImpl来让用户自定义相关配置，并提供了四个实现类JtaProcessEngineConfiguration, SpringProcessEngineConfiguration, StandaloneInMemProcessEngineConfiguration, StandaloneProcessEngineConfiguration，若要执行初始化达梦配置的方法，可重写类ProcessEngineConfigurationImpl中的buildProcessEngine方法，在流程引擎构建时完成，如下

public class MyProcessEngineConfigurationImpl extends SpringProcessEngineConfiguration {
    @Override
    public ProcessEngine buildProcessEngine() {
        // 初始化达梦配置
        InitDmConfig.init(databaseTypeMappings);

        return super.buildProcessEngine();
    }
}

在定义activiti引擎配置类的bean时，指定为我们重写的这个类即可