mybatis-generator多个数据库存在相同的表

mybatis-generator多个数据库存在相同的表

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问题现象

使用mybatis时难免会使用其提供的mybatis-generator生成默认的xml和实体类，今天我发现如果本地安装一个mysql，里面创建两个不同的数据库，而他们有相同的表，生成的实体类中可能是随机的。
比如我有一个数据库 ‘a’ 里面有一张表 ‘user’，我现在在建一个库‘b’，里面也有一张表‘user’，这样我生成代码时，虽然jdbcUrl配置的是a库，但生成的User实体类可能是b库里面的。

源码解析

查看其源码，下面是核心方法
org.mybatis.generator.internal.db.DatabaseIntrospector#getColumns

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private Map<ActualTableName, List<IntrospectedColumn>> getColumns(
        TableConfiguration tc) throws SQLException {
    String localCatalog;
    String localSchema;
    String localTableName;

    boolean delimitIdentifiers = tc.isDelimitIdentifiers()
            || stringContainsSpace(tc.getCatalog())
            || stringContainsSpace(tc.getSchema())
            || stringContainsSpace(tc.getTableName());

    if (delimitIdentifiers) {
        localCatalog = tc.getCatalog();
        localSchema = tc.getSchema();
        localTableName = tc.getTableName();
    } else if (databaseMetaData.storesLowerCaseIdentifiers()) {
        localCatalog = tc.getCatalog() == null ? null : tc.getCatalog()
                .toLowerCase();
        localSchema = tc.getSchema() == null ? null : tc.getSchema()
                .toLowerCase();
        localTableName = tc.getTableName().toLowerCase();
    } else if (databaseMetaData.storesUpperCaseIdentifiers()) {
        localCatalog = tc.getCatalog() == null ? null : tc.getCatalog()
                .toUpperCase();
        localSchema = tc.getSchema() == null ? null : tc.getSchema()
                .toUpperCase();
        localTableName = tc.getTableName().toUpperCase();
    } else {
        localCatalog = tc.getCatalog();
        localSchema = tc.getSchema();
        localTableName = tc.getTableName();
    }

    if (tc.isWildcardEscapingEnabled()) {
        String escapeString = databaseMetaData.getSearchStringEscape();

        if (localSchema != null) {
            localSchema = escapeName(localSchema, escapeString);
        }

        localTableName = escapeName(localTableName, escapeString);
    }

    Map<ActualTableName, List<IntrospectedColumn>> answer = new HashMap<>();

    if (logger.isDebugEnabled()) {
        String fullTableName = composeFullyQualifiedTableName(localCatalog, localSchema,
                        localTableName, '.');
        logger.debug(getString("Tracing.1", fullTableName)); //$NON-NLS-1$
    }

    ResultSet rs = databaseMetaData.getColumns(localCatalog, localSchema,
            localTableName, "%"); //$NON-NLS-1$

    boolean supportsIsAutoIncrement = false;
    boolean supportsIsGeneratedColumn = false;
    ResultSetMetaData rsmd = rs.getMetaData();
    int colCount = rsmd.getColumnCount();
    for (int i = 1; i <= colCount; i++) {
        if ("IS_AUTOINCREMENT".equals(rsmd.getColumnName(i))) { //$NON-NLS-1$
            supportsIsAutoIncrement = true;
        }
        if ("IS_GENERATEDCOLUMN".equals(rsmd.getColumnName(i))) { //$NON-NLS-1$
            supportsIsGeneratedColumn = true;
        }
    }

    while (rs.next()) {
        IntrospectedColumn introspectedColumn = ObjectFactory
                .createIntrospectedColumn(context);

        introspectedColumn.setTableAlias(tc.getAlias());
        introspectedColumn.setJdbcType(rs.getInt("DATA_TYPE")); //$NON-NLS-1$
        introspectedColumn.setActualTypeName(rs.getString("TYPE_NAME")); //$NON-NLS-1$
        introspectedColumn.setLength(rs.getInt("COLUMN_SIZE")); //$NON-NLS-1$
        introspectedColumn.setActualColumnName(rs.getString("COLUMN_NAME")); //$NON-NLS-1$
        introspectedColumn
                .setNullable(rs.getInt("NULLABLE") == DatabaseMetaData.columnNullable); //$NON-NLS-1$
        introspectedColumn.setScale(rs.getInt("DECIMAL_DIGITS")); //$NON-NLS-1$
        introspectedColumn.setRemarks(rs.getString("REMARKS")); //$NON-NLS-1$
        introspectedColumn.setDefaultValue(rs.getString("COLUMN_DEF")); //$NON-NLS-1$

        if (supportsIsAutoIncrement) {
            introspectedColumn.setAutoIncrement(
                    "YES".equals(rs.getString("IS_AUTOINCREMENT"))); //$NON-NLS-1$ //$NON-NLS-2$
        }

        if (supportsIsGeneratedColumn) {
            introspectedColumn.setGeneratedColumn(
                    "YES".equals(rs.getString("IS_GENERATEDCOLUMN"))); //$NON-NLS-1$ //$NON-NLS-2$
        }

        ActualTableName atn = new ActualTableName(
                rs.getString("TABLE_CAT"), //$NON-NLS-1$
                rs.getString("TABLE_SCHEM"), //$NON-NLS-1$
                rs.getString("TABLE_NAME")); //$NON-NLS-1$

        List<IntrospectedColumn> columns = answer.computeIfAbsent(atn, k -> new ArrayList<>());

        columns.add(introspectedColumn);

        if (logger.isDebugEnabled()) {
            logger.debug(getString(
                    "Tracing.2", //$NON-NLS-1$
                    introspectedColumn.getActualColumnName(), Integer
                            .toString(introspectedColumn.getJdbcType()),
                    atn.toString()));
        }
    }

    closeResultSet(rs);

    if (answer.size() > 1
            && !stringContainsSQLWildcard(localSchema)
            && !stringContainsSQLWildcard(localTableName)) {
        // issue a warning if there is more than one table and
        // no wildcards were used
        ActualTableName inputAtn = new ActualTableName(tc.getCatalog(), tc
                .getSchema(), tc.getTableName());

        StringBuilder sb = new StringBuilder();
        boolean comma = false;
        for (ActualTableName atn : answer.keySet()) {
            if (comma) {
                sb.append(',');
            } else {
                comma = true;
            }
            sb.append(atn.toString());
        }

        warnings.add(getString("Warning.25", //$NON-NLS-1$
                inputAtn.toString(), sb.toString()));
    }

    return answer;
}

上面方法内容有点多，核心逻辑就是

  1. 根据CataLog，Schema，TableName三个属性从databaseMetaData里面获取ResultSet。

    ResultSet rs = databaseMetaData.getColumns(localCatalog, localSchema,localTableName, “%”);

  2. 遍历上面的结果集，按照结果集返回值里面的 TABLE_CAT ， TABLE_SCHEM ， TABLE_NAME 存入到answer里。

    ActualTableName atn = new ActualTableName(
    rs.getString(“TABLE_CAT”), //$NON-NLS-1$
    rs.getString(“TABLE_SCHEM”), //$NON-NLS-1$
    rs.getString(“TABLE_NAME”)); //$NON-NLS-1$

  3. 返回 answer对象。

    因为我们我先前没有指定catalog 和 scheme，这里的REsultSet里会获取a库和b库中的user表，即两张表都会返回。

解决办法

添加 属性，不要从metadata中获取其他数据库的表

改动前

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<jdbcConnection driverClass="com.mysql.jdbc.Driver"
                connectionURL="${jdbc.url}"
                userId="${jdbc.username}"
                password="${jdbc.password}">
</jdbcConnection>

改动后

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<jdbcConnection driverClass="com.mysql.jdbc.Driver"
                connectionURL="${jdbc.url}"
                userId="${jdbc.username}"
                password="${jdbc.password}">
    <property name="nullCatalogMeansCurrent" value="true"/>
</jdbcConnection>

参考

https://mybatis.org/generator/usage/mysql.html

https://github.com/mybatis/generator/issues/622

#mybatis #bug #generator
mybatis-generator多个数据库存在相同的表
https://www.huangchaoyu.com/875549236.html
作者
hcy
发布于
2021年7月17日
更新于
2024年8月17日
许可协议