Retrieving a list of values across databases with mybatis

I have 2 Java POJO files

class Filter Variables {
private String id;
private String name;
private List<ValueVariables> variableValues;
getters() setters()
}

class ValueVariables {
private String id;
private String valueListId;
private String value;
}

The database has a FK mapping between FilterVariable.id and ValueVariable.valueListId. Inserts into the table work perfectly, i have a single transaction that inserts into both tables separately. While retrieving the data using select and join, I only receive the first row from the table in the database.

Database Tables:

CREATE TABLE IF NOT EXISTS filter_variables (
id VARCHAR(36) NOT NULL,
name VARCHAR(30) NOT NULL,
PRIMARY KEY(id)
);

CREATE TABLE IF NOT EXISTS variable_values (
id INT(10) NOT NULL AUTO_INCREMENT,
valueListId VARCHAR(36) NOT NULL,
value VARCHAR(100) NOT NULL,
PRIMARY KEY(id),
FOREIGN KEY (valueListId) REFERENCES filter_variables(id)
);

<select id="selectFilterVariableById" parameterType="java.lang.String" resultMap="FilterVariablesJoinResultMap">
    select FV.id, FV.name, VV.value, VV.valueListId
    from filter_variables as FV left outer join variable_values as VV ON FV.id=VV.valueListId
    where FV.id = #{id,jdbcType=VARCHAR}
</select>

The method in the interface is defined as List<FilterVariables> selectFilterVariableById(String id); I understand that with 2 separate I can store values into the two Pojo and use them, but is there any way with joins where I can retrieve multiple rows?

The result map is defined as so:

<resultMap id="FilterVariablesJoinResultMap" type="com.example.mybatissample.FilterVariables">
    <id column="id" jdbcType="VARCHAR" property="id" />
    <result column="name" jdbcType="VARCHAR" property="name" />
    <collection property="variableValues" ofType="com.example.mybatissample.ValueVariables">
      <id property="id" column="id"/>
      <result property="valueListId" column="valueListId"/>
      <result property="value" column="value"/>
    </collection>
</resultMap>

This is how the data in mysql looks like.

When a request is made from Java:

List<FilterVariables> vals= filterVariablesMapper.selectFilterVariableById(id);
System.out.println(vals);
System.out.println(vals.size());

I only get the first row

[FilterVariables [id=b218df5c-eac1-4e01-846a-119345bb254d, name=ME, valueId=null, storageRecordType=null, values={b218df5c-eac1-4e01-846a-119345bb254d test@mailinator.com}]]

1

Answer

As mentioned by @ave, the solution is to either

Remove the from the collection – degrades performance
Just rename the variable used in – Implementation below:

The result map is now:

<resultMap id="FilterVariablesJoinResultMap" type="com.example.mybatissample.FilterVariables">
    <id column="id" jdbcType="VARCHAR" property="id" />
    <result column="name" jdbcType="VARCHAR" property="name" />
    <collection property="variableValues" ofType="com.example.mybatissample.ValueVariables">
      <id property="varId" column="varId"/>
      <result property="valueListId" column="valueListId"/>
      <result property="value" column="value"/>
    </collection>
</resultMap>

With this the results come as required.

ValueVariable is now:

class ValueVariables {
private String varId;
private String valueListId;
private String value;
getters() and setters()
}

The select query is now:

<select id="selectFilterVariableById" parameterType="java.lang.String" resultMap="FilterVariablesJoinResultMap">

    select FV.id, name, description, type, columnId, storageRecordType, valueId,
    operator, dbId, sharedValue, systemVariable, VV.id as varId, VV.value, VV.valueListId
    from filter_variables as FV left outer join variable_values as VV ON FV.id=VV.valueListId
    where FV.id = #{id,jdbcType=VARCHAR}
  </select>

Please note that VV.id is to be aliased for this to work.

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Answer