先上結(jié)論

• Mysql 對語句的長度有限制，默認是 4M。
• Mybatis 對動態(tài)語句沒有數(shù)量上的限制。

Mysql修改長度限制

# 查詢當前大小
mysql> select @@max_allowed_packet;
+----------------------+
| @@max_allowed_packet |
+----------------------+
|              4194304 |
+----------------------+
1 row in set (0.00 sec)

# 修改為256M
mysql> SET GLOBAL max_allowed_packet=268435456;
Query OK, 0 rows affected (0.00 sec)

# 退出客戶端重新登錄
mysql> select @@max_allowed_packet;
+----------------------+
| @@max_allowed_packet |
+----------------------+
|            268435456 |
+----------------------+
1 row in set (0.00 sec)

Mybatis 解析動態(tài)SQL的源碼。

// 開始解析
public void parse() {
    if (!configuration.isResourceLoaded(resource)) {
        configurationElement(parser.evalNode("/mapper"));
        configuration.addLoadedResource(resource);
        bindMapperForNamespace();
    }

    parsePendingResultMaps();
    parsePendingChacheRefs();
    parsePendingStatements();
}
// 解析mapper
private void configurationElement(XNode context) {
    try {
        String namespace = context.getStringAttribute("namespace");
        if (namespace.equals("")) {
            throw new BuilderException("Mapper's namespace cannot be empty");
        }
        builderAssistant.setCurrentNamespace(namespace);
        cacheRefElement(context.evalNode("cache-ref"));
        cacheElement(context.evalNode("cache"));
        parameterMapElement(context.evalNodes("/mapper/parameterMap"));
        resultMapElements(context.evalNodes("/mapper/resultMap"));
        sqlElement(context.evalNodes("/mapper/sql"));
        buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
    } catch (Exception e) {
        throw new BuilderException("Error parsing Mapper XML. Cause: " + e, e);
    }
}

// 創(chuàng)建 select|insert|update|delete 語句
private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
    for (XNode context : list) {
        final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
        try {
            statementParser.parseStatementNode();
        } catch (IncompleteElementException e) {
            configuration.addIncompleteStatement(statementParser);
        }
    }
}

// 填充參數(shù)，創(chuàng)建語句
public BoundSql getBoundSql(Object parameterObject) {
    DynamicContext context = new DynamicContext(configuration, parameterObject);
    rootSqlNode.apply(context);
    SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
    Class<?> parameterType = parameterObject == null ? Object.class : parameterObject.getClass();
    SqlSource sqlSource = sqlSourceParser.parse(context.getSql(), parameterType, context.getBindings());
    BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
    for (Map.Entry<String, Object> entry : context.getBindings().entrySet()) {
        boundSql.setAdditionalParameter(entry.getKey(), entry.getValue());
    }
    return boundSql;
}

從開始到結(jié)束， Mybatis 都沒有對填充的條數(shù)和參數(shù)的數(shù)量做限制。