MyBatis 可以不用執行就生成 Dynamic SQL 嗎？

Question

我有一些復雜的查詢要用一些可選的過濾器來構建，MyBatis 似乎是生成動態 SQL 的理想候選者。

但是，我仍然希望我的查詢在與應用程序（未使用 MyBatis）的 rest 相同的框架中執行。

所以我希望做的是嚴格使用 MyBatis 來生成 SQL，但是從那里使用我的應用程序的 rest 來實際執行它。 這可能嗎？ 如果是這樣，如何？

Answer 1

雖然MyBatis設計用於在構建查詢后執行查詢，但您可以利用它的配置和一些“內部知識”來獲得所需內容。

MyBatis是一個非常好的框架，遺憾的是它缺少文檔方面，因此源代碼是你的朋友。 如果你四處挖掘，你應該碰到這些類： org.apache.ibatis.mapping.MappedStatement和org.apache.ibatis.mapping.BoundSql ，它們是構建動態SQL的關鍵角色。 這是一個基本的用法示例：

具有此數據的MySQL表user ：

name    login
-----   -----
Andy    a
Barry   b
Cris    c

User類：

package pack.test;
public class User {
    private String name;
    private String login;
    // getters and setters ommited
}

UserService接口：

package pack.test;
public interface UserService {
    // using a different sort of parameter to show some dynamic SQL
    public User getUser(int loginNumber);
}

UserService.xml映射文件：

<mapper namespace="pack.test.UserService">
    <select id="getUser" resultType="pack.test.User" parameterType="int">
       <!-- dynamic change of parameter from int index to login string -->
       select * from user where login = <choose>
                                           <when test="_parameter == 1">'a'</when>
                                           <when test="_parameter == 2">'b'</when>
                                           <otherwise>'c'</otherwise>
                                        </choose>   
    </select>
</mapper>

sqlmap-config.file ：

<configuration>
    <settings>
        <setting name="lazyLoadingEnabled" value="false" />
    </settings>
    <environments default="development"> 
        <environment id="development"> 
            <transactionManager type="JDBC"/> 
            <dataSource type="POOLED"> 
                <property name="driver" value="com.mysql.jdbc.Driver"/> 
                <property name="url" value="jdbc:mysql://localhost/test"/> 
                <property name="username" value="..."/> 
                <property name="password" value="..."/> 
            </dataSource> 
        </environment> 
      </environments>
    <mappers>
        <mapper resource="pack/test/UserService.xml"/>
    </mappers>
</configuration>

AppTester顯示結果：

package pack.test;

import java.io.Reader;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class AppTester {
    private static String CONFIGURATION_FILE = "sqlmap-config.xml";

    public static void main(String[] args) throws Exception {
        Reader reader = null;
        SqlSession session = null;
        try {

            reader = Resources.getResourceAsReader(CONFIGURATION_FILE);
            session = new SqlSessionFactoryBuilder().build(reader).openSession();
            UserService userService = session.getMapper(UserService.class);

            // three users retreived from index
            for (int i = 1; i <= 3; i++) {
                User user = userService.getUser(i);
                System.out.println("Retreived user: " + user.getName() + " " + user.getLogin());

                // must mimic the internal statement key for the mapper and method you are calling
                MappedStatement ms = session.getConfiguration().getMappedStatement(UserService.class.getName() + ".getUser");
                BoundSql boundSql = ms.getBoundSql(i); // parameter for the SQL statement
                System.out.println("SQL used: " + boundSql.getSql());
                System.out.println();
            }

        } finally {
            if (reader != null) {
                reader.close();
            }
            if (session != null) {
                session.close();
            }
        }
    }
}

結果如下：

Retreived user: Andy a
SQL used: select * from user where login =  'a'

Retreived user: Barry b
SQL used: select * from user where login =  'b'

Retreived user: Cris c
SQL used: select * from user where login =  'c'

Answer 2

每個人都知道如何使用BoundSql.getSql（）從MyBatis獲取一個參數化的查詢字符串，如下所示：

// get parameterized query
MappedStatement ms = configuration.getMappedStatement("MyMappedStatementId");
BoundSql boundSql = ms.getBoundSql(parameters);
System.out.println("SQL" + boundSql.getSql());
// SELECT species FROM animal WHERE name IN (?, ?) or id = ?

但是現在您需要方程的另一半，即與問號對應的值列表：

// get parameters
List<ParameterMapping> boundParams = boundSql.getParameterMappings();
String paramString = "";
for(ParameterMapping param : boundParams) {
    paramString += boundSql.getAdditionalParameter(param.getProperty()) + ";";
}
System.out.println("params:" + paramString);
// "Spot;Fluffy;42;"

現在，您可以將其序列化以發送到其他位置以進行運行，或者您可以將其打印到日志中，以便將它們拼接在一起並手動運行查詢。

*未經測試的代碼，可能是次要類型問題等

Answer 3

public static void main(String[] args) throws Exception {

    String script = "<script>select * from table where 1 = 1<if test='id != null'>and id = ${id} </if></script>";

    System.out.println(buildSql(script));

}

private static String buildSql(String script) {

    LanguageDriver languageDriver = new XMLLanguageDriver();

    Configuration configuration = new Configuration();

    SqlSource sqlSource = languageDriver.createSqlSource(configuration, script, Object.class);

    Map<String, String> parameters = new HashMap<>();
    parameters.put("id", "1");

    BoundSql boundSql = sqlSource.getBoundSql(parameters);

    return boundSql.getSql();

}

使用 ${id} 而不是 #{id}

結果是：select * 來自表，其中 1 = 1 且 id = 1

Answer 4

只是添加到Bogdan的正確答案：如果您的接口具有更復雜的簽名，則需要將JavaBean傳遞給getBoundSql()其中getter用於接口參數。

假設您要根據登錄號和/或用戶名查詢用戶。 您的界面可能如下所示：

package pack.test;
public interface UserService {
    // using a different sort of parameter to show some dynamic SQL
    public User getUser(@Param("number") int loginNumber, @Param("name") String name);
}

我省略了Mapper代碼，因為它與此討論無關，但AppTester中的代碼應該變為：

[...]
final String name = "Andy";
User user = userService.getUser(i, name);
System.out.println("Retreived user: " + user.getName() + " " + user.getLogin());

// must mimic the internal statement key for the mapper and method you are calling
MappedStatement ms  = session.getConfiguration().getMappedStatement(UserService.class.getName() + ".getUser");
BoundSql boundSql = ms.getBoundSql(new Object() {
   // provide getters matching the @Param's in the interface declaration
   public Object getNumber() {
     return i;
   }
   public Object getName() {
     return name;
   }

});
System.out.println("SQL used: " + boundSql.getSql());
System.out.println();
[...]

Answer 5

mybatis版本是3.4.5

Util類

要將mapper轉換為sql，需要mapper接口類，方法名，參數和sqlSession。

        package util;

        import java.lang.reflect.Method;
        import java.text.DateFormat;
        import java.time.LocalDateTime;
        import java.time.format.DateTimeFormatter;
        import java.util.Date;
        import java.util.List;
        import java.util.Locale;
        import java.util.regex.Matcher;
        import org.apache.ibatis.binding.MapperMethod.MethodSignature;
        import org.apache.ibatis.mapping.BoundSql;
        import org.apache.ibatis.mapping.MappedStatement;
        import org.apache.ibatis.mapping.ParameterMapping;
        import org.apache.ibatis.reflection.MetaObject;
        import org.apache.ibatis.session.Configuration;
        import org.apache.ibatis.session.SqlSession;
        import org.apache.ibatis.type.TypeHandlerRegistry;
        import org.springframework.util.CollectionUtils;

        /**
         * @author zwxbest - 19-4-25
         */
        public class SqlUtil {

            public static String showSql(SqlSession sqlSession, Class mapperInterface, String methodName,
                Object[] params) {
                Configuration configuration = sqlSession.getConfiguration();
                MappedStatement ms = configuration.getMappedStatement(
                    mapperInterface.getName() + "." + methodName);

                Method sqlMethod = null;

                //find method equals methodName
                for (Method method : mapperInterface.getDeclaredMethods()) {
                    if (method.getName().equals(methodName)) {
                        sqlMethod = method;
                        break;
                    }
                }
                if (sqlMethod == null) {
                    throw new RuntimeException("mapper method is not found");
                }

                MethodSignature method = new MethodSignature(configuration, mapperInterface, sqlMethod);
                Object paramObject = method.convertArgsToSqlCommandParam(params);
                BoundSql boundSql = ms.getBoundSql(paramObject);
                Object parameterObject = boundSql.getParameterObject();
                List<ParameterMapping> parameterMappings = boundSql
                    .getParameterMappings();
                String sql = boundSql.getSql().replaceAll("[\\s]+", " ");
                if (!CollectionUtils.isEmpty(parameterMappings) && parameterObject != null) {
                    TypeHandlerRegistry typeHandlerRegistry = configuration
                        .getTypeHandlerRegistry();
                    if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
                        sql = sql.replaceFirst("\\?",
                            Matcher.quoteReplacement(getParameterValue(parameterObject)));
                    } else {
                        MetaObject metaObject = configuration.newMetaObject(
                            parameterObject);
                        for (ParameterMapping parameterMapping : parameterMappings) {
                            String propertyName = parameterMapping.getProperty();
                            if (metaObject.hasGetter(propertyName)) {
                                Object obj = metaObject.getValue(propertyName);
                                sql = sql
                                    .replaceFirst("\\?", Matcher.quoteReplacement(getParameterValue(obj)));
                            } else if (boundSql.hasAdditionalParameter(propertyName)) {
                                Object obj = boundSql.getAdditionalParameter(propertyName);
                                sql = sql
                                    .replaceFirst("\\?", Matcher.quoteReplacement(getParameterValue(obj)));
                            } else {
                                sql = sql.replaceFirst("\\?", "missing");
                            }
                        }
                    }
                }
                return sql;
            }

            /**
             * if param's type is `String`,add single quotation<br>
             *
             * if param's type is `datetime`,convert to string and quote <br>
             */
            private static String getParameterValue(Object obj) {
                String value = null;
                if (obj instanceof String) {
                    value = "'" + obj.toString() + "'";
                } else if (obj instanceof Date) {
                    DateFormat formatter = DateFormat
                        .getDateTimeInstance(DateFormat.DEFAULT, DateFormat.DEFAULT, Locale.CHINA);
                    value = "'" + formatter.format(new Date()) + "'";
                } else if (obj instanceof LocalDateTime) {
                    value = "\'" + ((LocalDateTime) obj)
                        .format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")) + "\'";
                } else {
                    if (obj != null) {
                        value = obj.toString();
                    } else {
                        value = "";
                    }

                }
                return value;
            }
}

電話示例

sqlSession由Spring注入。

@Autowired
private SqlSession sqlSession;

    String sql = SqlUtil
        .showSql(sqlSession, PromotionCodeMapper.class, "selectByPromotionCodeForUpdate",
            new Object[]{"111"});
    log.warn(sql);