MyBatis - how to create w dynamic WHERE Clause

The service gets an unknown object containing a list of three values [column, operator, value] For example, EMAIL - like - "TEST"

Based on the resulting list to build the WHERE clause I have but I would also be able to build such a condition as follows (for example)

WHERE (email like 'test' AND user_id <> 5) OR (trans_id <100 AND session_id> 500)

Does anyone can help me how to do it?

回答1:

I have been rediscovering MyBatis after a long absence myself (I was familiar with iBatis at one time). Rolf's example looks like it might be the .Net implementation, I may be wrong but I don't think the Java notation looks like that now. Rolf's tip about the literal strings is very useful.

I've created a little class to hold your columns, operators and value and pass these into MyBatis to do the processing. The columns and operators are string literals but I have left the values as sql parameters (I imagine MyBatis would be able to do any necessary type conversion).

public class TestAnswer {
    public static void main(String[] args) {
            ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
            SqlSessionFactory sqlFactory = (SqlSessionFactory) ctx.getBean("sqlSessionFactory");            
            MappedStatement statement = sqlFactory.getConfiguration().getMappedStatement("testAnswer");                        

            ArrayList<Clause> params1 = new ArrayList<Clause>();
            params1.add(new Clause("email","like","test"));
            params1.add(new Clause("user","<>",5));

            ArrayList<Clause> params2 = new ArrayList<Clause>();
            params2.add(new Clause("trans_id","<",100));
            params2.add(new Clause("session_id",">",500));

            HashMap params = new HashMap();
            params.put("params1", params1);
            params.put("params2", params2);

            BoundSql boundSql = statement.getBoundSql(params);
            System.out.println(boundSql.getSql());             
    }

    static class Clause{        
        private String column;
        private String operator;
        private Object value;

        public Clause(String column, String operator, Object value){
            this.column = column;
            this.operator = operator;
            this.value = value;
        }

        public void setColumn(String column) {this.column = column;}
        public void setOperator(String operator) {this.operator = operator;}
        public void setValue(Object value) {this.value = value;}
        public String getColumn() {return column;}
        public String getOperator() {return operator;}
        public Object getValue() {return value;}        
    }    
}

As you can see, I use Spring but I expect something similar would probably work outside of the Spring environment.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

    <mapper namespace="com.stackoverflow.TestMapper">

    <select id="testAnswer" parameterType="map" resultType="hashmap">
      select *
    FROM somewhere
        <where>
            <foreach item="clause" collection="params1" separator=" AND " open="(" close=")"> 
                ${clause.column} ${clause.operator} #{clause.value} 
            </foreach>            
            OR
            <foreach item="clause" collection="params2" separator=" AND " open="(" close=")"> 
                ${clause.column} ${clause.operator} #{clause.value} 
            </foreach>    
        </where>
    </select>

</mapper>

回答2:

There are two key parts to this answer. One is the "dynamic" element, and the other are the $$ literal elements around the "operator" in your question.

  <select id="yourSelect" parameterClass="Map" resultMap="somethingsomething" >
    select * from YOURTABLE
      <dynamic prepend="WHERE">
        <isNotNull prepend="AND" property="email">
          email $operator$ #testvalue#
        </isNotNull>
      </dynamic>
  </select>

See also the DataMapper Dynamic SQL documentation on this topic.