[Mybatis source of learning] parameter processing mybatis

A parameter and the parameter value of the processing mybatis

1, a single parameter

• mybatis no treatment

• Value ways:

  # {Parameter name / arbitrary name}

<!-- Employee getEmpById(Integer id);  -->
<select id="getEmpById" resultType="com.mxc.bean.Employee">
    select * from employee where id=#{id}
</select>

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2, a plurality of parameters

• mybatis will be packaged as a plurality of parameters to automatically map

  key: param1, ..., paramN, may be 0, ..., N-1 (i.e., the parameter index, N is the number of parameters)

  value: Parameter Value

• Value ways:

  The above-described key} {#

<!-- Employee getEmpByIdAndLastName(Integer id, String lastName);  -->
<select id="getEmpByIdAndLastName" resultType="com.mxc.bean.Employee">
    select * from employee where id=#{param1} and last_name=#{param2}
</select>

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Assigning clear key for multiple parameters

• @ParamAnnotation key may specify an explicit parameter, the parameter values ​​for easy access in the sql

• Value ways:

  # {@ Param annotation specified key}

<!-- Employee getEmpByIdAndLastName(@Param("id")Integer id, @Param("lastName")String lastName);  -->
<select id="getEmpByIdAndLastName" resultType="com.mxc.bean.Employee">
    select * from employee where id=#{id} and last_name=#{lastName}
</select>

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Long encapsulates parameters map, easy to take the value of the parameter used to specify the use of the package key @Param

 

3, the parameter is a POJO

• If the plurality of parameters is exactly the POJO attribute value may be directly into a POJO

• Value ways:

  Attribute name} {#

<!-- Employee getEmpByIdAndLastName(Employee emp);  -->
<select id="getEmpByIdAndLastName" resultType="com.mxc.bean.Employee">
    select * from employee where id=#{id} and last_name=#{lastName}
</select>

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4, the argument is a Map

• If the parameter is not one of the plurality of POJO properties, it may be packaged as a Map

• Value ways:

  ​ #{Map的key}

<!-- 
    Employee getEmpByIdAndLastName(Map<String, Object> map); 
    map：
        Map<String, Object> map = new HashMap<>();
        map.put("id", 1);
        map.put("lastName", "mxc");
-->
<select id="getEmpByIdAndLastName" resultType="com.mxc.bean.Employee">
    select * from employee where id=#{id} and last_name=#{lastName}
</select>

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Small scale chopper

Employee getEmp(@Param("id")Integer id,String lastName);
// 取值：id=>#{id/param1}，lastName=>#{param2}

Employee getEmp(Integer id,@Param("e")Employee emp);
// 取值：id=>#{param1}，lastName => #{param2.lastName/e.lastName}

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$ # {} {} And the similarities and differences of
the same:

Value can be obtained in the map object property value or pojo

different:

# {}: Is pre-compiled form, set the parameter to the sql statement, sql injection can be prevented
$ {}: value taken directly assembled in the sql statement, there will be safety problems
usage scene

In most cases, taking the value of the parameter using # {}. {} $ Can be used in places not support native JDBC placeholders. As by year table query: select * from $ {year} _salary;

Second, the source processing parameters to achieve mybatis

1, an internal data structure

Package com.spring.test.service.mybatis; 

Import org.apache.ibatis.builder.ParameterExpression; 

/ ** 
 * 
 * / 
public  class paramHandler { 

    public  static  void main (String [] args) { 
        paramsTokenHandler (); 
    } 


    / * * 
     * method name: list <the User> queryList (String name, RowBounds RowBounds, int Age, @Param ( "address") String addresss); 
     * internal parameter mapping: 
     * MethodSignature.SortedMap <Integer, String> params 
     * parameter list subscript -> parameter name (if it is @Param, it shows notes of value, otherwise the current number of parameters in addition to ranking RowBounds, ResultHandler for the parameter list) 
     * 0-> 0 
     * 2-> 1 
     * 3-> address
     *
     * MethodSignature.convertArgsToSqlCommandParam (Object [] args) Returns: paramMap 
     * 
     * paramMap internal memory as follows: 
     * the parameter names -> parameters subscript 
     * 0-> name value 
     * 1-> age values 
     * Address-> addresss of values 
     * 
     * param1-> name value 
     * param2-> age value 
     value * param3-> addresss of 
     * 
     * / 
    public  static  void paramsToParamMap () { 

    } 

    / ** 
     * examples: # {checkedTime, jdbcType = BIGINT , typeHandler = com. } meituan.payment.fundsgateway.core.model.handler.DateForLongTypeHandler 
     * / 
    public  static  void paramsTokenHandler () {
        String token="checkedTime,jdbcType=BIGINT,typeHandler=com.meituan.payment.fundsgateway.core.model.handler.DateForLongTypeHandler";
        ParameterExpression parameterExpression=new ParameterExpression(token);
        String name=parameterExpression.get("property");
        System.out.println(name);
        String jdbcType=parameterExpression.get("jdbcType");
        System.out.println(jdbcType);
        String typeHandler=parameterExpression.get("typeHandler");
        System.out.println(typeHandler);
    }
}

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2, the special data structures and algorithms involved

org.apache.ibatis.scripting.defaults.DefaultParameterHandler

=> Sql resolved by looping through ParameterMapping obtain a specified value from the argument list, provided to the sql statement? Placeholders.

 

org.apache.ibatis.reflection.MetaObject

=> A method of packaging into a parameter list MetaObject, provides a method of obtaining uniform parameter value

 

org.apache.ibatis.reflection.property.PropertyTokenizer

=> # {PropertyName} placeholder in propertyName MetaObject acquired according to sql statement sql statement? Value.

 

org.apache.ibatis.builder.SqlSourceBuilder

org.apache.ibatis.builder.ParameterMappingTokenHandler

org.apache.ibatis.parsing.GenericTokenParser

org.apache.ibatis.builder.ParameterExpression

=> Sql statement in the {} # replace? , And parse the List <ParameterMapping>