Mybatis source code analysis parameter processing

Mybatis’ handling of parameters is worth careful consideration, otherwise a series of errors will occur in the process of using directly confused.

In the past, WHEN I encountered a parameter binding error, I simply annotated @param and solved it, but then I ran into some problems that disproved my assumption that @param was not necessary for a single parameter. This raises a question, how exactly does Mybatis handle parameters?

Several common scenarios:

• A single parameter
• • No annotations, based on references to ${} and #{}, both primitive types and custom objects work
• • Without annotations, list and array are not allowed due to the use of foreach tags
• • Without annotations, base type Boolean also fails based on the if tag

A preliminary packaging

The first processing is in MapperMethod:

private Object getParam(Object[] args) { final int paramCount = paramPositions.size(); if (args == null || paramCount == 0) { return null; } else if (! hasNamedParameters && paramCount == 1) { return args[paramPositions.get(0)]; } else { Map<String, Object> param = new MapperParamMap<Object>(); for (int i = 0; i < paramCount; i++) { param.put(paramNames.get(i), args[paramPositions.get(i)]); } // issue #71, add param names as param1, param2... but ensure backward compatibility for (int i = 0; i < paramCount; i++) { String genericParamName = "param" + String.valueOf(i + 1); if (! param.containsKey(genericParamName)) { param.put(genericParamName, args[paramPositions.get(i)]); } } return param; }}Copy the code

There are three possibilities: null, object[], and MapperParamMap. The third one constructs the common param1, parm2…

AuthAdminUser findAuthAdminUserByUserId (@ Param (” userId “) String userId);

When we define this in the Mapper interface, we follow the else code block above, and the MapperParamMap will contain two elements, one key with userId and the other param1.

The second processing is to wrap the arguments as a collection when calling executor’s Query method in DefaultSqlSession:

private Object wrapCollection(final Object object) { if (object instanceof List) { StrictMap<Object> map = new StrictMap<Object>(); map.put("list", object); return map; } else if (object ! = null && object.getClass().isArray()) { StrictMap<Object> map = new StrictMap<Object>(); map.put("array", object); return map; } return object; }Copy the code

Both MapperParamMap and StrictMap inherit from HashMap, except that an exception is thrown when super.containsKey(key) is set to false.

Present instance

List<String> selectFeeItemTypeNameByIds(List<Integer> itemIds);Copy the code

<select id="selectFeeItemTypeNameByIds" parameterType="java.util.List" resultType="java.lang.String">
    SELECT fee_item_type_name
    FROM tb_uhome_fee_item_type
    WHERE fee_item_type_id IN
    <foreach collection="itemIds" item="itemId" open="(" close=")" separator="," >
        #{itemId}
    </foreach>
</select>Copy the code

<foreach collection="list" item="itemId" open="(" close=")" separator="," >
    #{itemId}
</foreach>Copy the code

if (object instanceof List) {
  StrictMap<Object> map = new StrictMap<Object>();
  map.put("list", object);
  return map;
}Copy the code

List<Map<String, Object>> selectPayMethodListByPlatform(boolean excludeInner);Copy the code

<select id="selectPayMethodListByPlatform" resultType="java.util.HashMap" parameterType="boolean">
    select a.`NAME`as payMethodName, a.`VALUE` as payMethod
    from tb_fcs_dictionary a
    where a.`CODE` = 'PAY_METHOD'
    and a.`STATUS` = 1
    and a.TYPE = 'PLATFORM'
    <if test="excludeInner">
        and a.value not in (14,98)
    </if>
</select>Copy the code

public Iterable<? > evaluateIterable(String expression, Object parameterObject) { try { Object value = OgnlCache.getValue(expression, parameterObject); if (value == null) throw new SqlMapperException("The expression '" + expression + "' evaluated to a null value."); if (value instanceof Iterable) return (Iterable<? >) value; if (value.getClass().isArray()) { // the array may be primitive, so Arrays.asList() may throw // a ClassCastException (issue 209). Do the work manually // Curse primitives! :) (JGB) int size = Array.getLength(value); List<Object> answer = new ArrayList<Object>(); for (int i = 0; i < size; i++) { Object o = Array.get(value, i); answer.add(o); } return answer; } throw new BuilderException("Error evaluating expression '" + expression + "'. Return value (" + value + ") was not iterable."); } catch (OgnlException e) { throw new BuilderException("Error evaluating expression '" + expression + "'. Cause: " + e, e); }}Copy the code

public boolean evaluateBoolean(String expression, Object parameterObject) { try { Object value = OgnlCache.getValue(expression, parameterObject); if (value instanceof Boolean) return (Boolean) value; if (value instanceof Number) return ! new BigDecimal(String.valueOf(value)).equals(BigDecimal.ZERO); return value ! = null; } catch (OgnlException e) { throw new BuilderException("Error evaluating expression '" + expression + "'. Cause: " + e, e); }}Copy the code

The actual processing

In the getBoundSql method of DynamicSqlSource:

• Parameter binding
  
  
  

  DynamicContext context = new DynamicContext(configuration, parameterObject);

public DynamicContext(Configuration configuration, Object parameterObject) { if (parameterObject ! = null && ! (parameterObject instanceof Map)) { MetaObject metaObject = configuration.newMetaObject(parameterObject); bindings = new ContextMap(metaObject); } else { bindings = new ContextMap(null); } bindings.put(PARAMETER_OBJECT_KEY, parameterObject); bindings.put(DATABASE_ID_KEY, configuration.getDatabaseId()); }Copy the code

• Node level by level processing (various tags and ${} processing)

rootSqlNode.apply(context);

This is the key to handling dynamic SQL by stripping out if, Choose, and foreach and using OGNL expressions to get the values of related attributes, such as the foreach and IF tags mentioned above.

It is then converted to simple text, and ${param} is finally processed in TextSqlNode, replacing it with the actual parameter value.

The replacement is as follows:

public String handleToken(String content) { try { Object parameter = context.getBindings().get("_parameter"); if (parameter == null) { context.getBindings().put("value", null); } else if (SimpleTypeRegistry.isSimpleType(parameter.getClass())) { context.getBindings().put("value", parameter); } Object value = OgnlCache.getValue(content, context.getBindings()); return (value == null ? "" : String.valueOf(value)); // issue #274 return "" instead of "null" } catch (OgnlException e) { throw new BuilderException("Error evaluating expression '" + content + "'. Cause: " + e, e); }}Copy the code

• Parameter parsing (#{} handling)

SqlSource sqlSource = sqlSourceParser.parse(context.getSql(), parameterType);

SqlSourceBuilder#parse:

public SqlSource parse(String originalSql, Class<? > parameterType) { ParameterMappingTokenHandler handler = new ParameterMappingTokenHandler(configuration, parameterType); GenericTokenParser parser = new GenericTokenParser("#{", "}", handler); String sql = parser.parse(originalSql); return new StaticSqlSource(configuration, sql, handler.getParameterMappings()); }Copy the code

The parse method of GenericTokenParser replaces #{xx} with? , the following SQL statement:

SELECT DISTINCT
    A.ORGAN_ID as organId,
    CONCAT(A. NAME, ' [', IFNULL(A.PY_NAME, ''), ']') as organName
FROM
    ORGAN A,
    ORGAN_REL B,
    V_USER_ORGAN C
WHERE
    A.ORGAN_ID = B.ORGAN_ID
AND B.ORGAN_CODE LIKE CONCAT(LEFT(C.ORGAN_CODE, 8), '%')
AND B.PAR_ID = 1
AND A.STATUS = 1
AND C.USER_ID = #{userId}Copy the code

After replacement:

SELECT DISTINCT
    A.ORGAN_ID as organId,
    CONCAT(A. NAME, ' [', IFNULL(A.PY_NAME, ''), ']') as organName
FROM
    ORGAN A,
    ORGAN_REL B,
    V_USER_ORGAN C
WHERE
    A.ORGAN_ID = B.ORGAN_ID
AND B.ORGAN_CODE LIKE CONCAT(LEFT(C.ORGAN_CODE, 8), '%')
AND B.PAR_ID = 1
AND A.STATUS = 1
AND C.USER_ID = ?Copy the code

Then construct a StaticSqlSource:

new StaticSqlSource(configuration, sql, handler.getParameterMappings());

This is just like using JDBC directly, using? As a placeholder.

Finally, we set the parameters in DefaultParameterHandler:

public void setParameters(PreparedStatement ps)
      throws SQLException {
    ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
    List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
    if (parameterMappings != null) {
      MetaObject metaObject = parameterObject == null ? null : configuration.newMetaObject(parameterObject);
      for (int i = 0; i < parameterMappings.size(); i++) {
        ParameterMapping parameterMapping = parameterMappings.get(i);
        if (parameterMapping.getMode() != ParameterMode.OUT) {
          Object value;
          String propertyName = parameterMapping.getProperty();
          PropertyTokenizer prop = new PropertyTokenizer(propertyName);
          if (parameterObject == null) {
            value = null;
          } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
            value = parameterObject;
          } else if (boundSql.hasAdditionalParameter(propertyName)) {
            value = boundSql.getAdditionalParameter(propertyName);
          } else if (propertyName.startsWith(ForEachSqlNode.ITEM_PREFIX)
              && boundSql.hasAdditionalParameter(prop.getName())) {
            value = boundSql.getAdditionalParameter(prop.getName());
            if (value != null) {
              value = configuration.newMetaObject(value).getValue(propertyName.substring(prop.getName().length()));
            }
          } else {
            value = metaObject == null ? null : metaObject.getValue(propertyName);
          }
          TypeHandler typeHandler = parameterMapping.getTypeHandler();
          if (typeHandler == null) {
            throw new ExecutorException("There was no TypeHandler found for parameter " + propertyName + " of statement " + mappedStatement.getId());
          }
          JdbcType jdbcType = parameterMapping.getJdbcType();
          if (value == null && jdbcType == null) jdbcType = configuration.getJdbcTypeForNull();
          typeHandler.setParameter(ps, i + 1, value, jdbcType);
        }
      }
    }
  }Copy the code

Here are five cases (the higher version incorporates the third and fourth) : – parameterObject is null and value is null. – parameterObject is of the type typeHandlerRegistry matches. Value is directly assigned to parameterObject. Through dynamic parameter values – parameters are dynamic and are in foreach (prefixed with FRCH), also through dynamic parameter values – complex objects or map types, through reflection

conclusion

List<String> selectFeeItemTypeNameByIds(List<Integer> itemIds);

List<Map<String, Object>> selectPayMethodListByPlatform(boolean excludeInner);Copy the code

public DynamicContext(Configuration configuration, Object parameterObject) { if (parameterObject ! = null && ! (parameterObject instanceof Map)) { MetaObject metaObject = configuration.newMetaObject(parameterObject); bindings = new ContextMap(metaObject); } else { bindings = new ContextMap(null); } bindings.put(PARAMETER_OBJECT_KEY, parameterObject); bindings.put(DATABASE_ID_KEY, configuration.getDatabaseId()); }Copy the code

key: "_parameter"  value: true
key: "_databaseId"  value: "MySQL"Copy the code

public Object get(Object key) { String strKey = (String) key; if (super.containsKey(strKey)) { return super.get(strKey); } if (parameterMetaObject ! = null) { Object object = parameterMetaObject.getValue(strKey); if (object ! = null) { super.put(strKey, object); } return object; } return null; }Copy the code

private Object getBeanProperty(PropertyTokenizer prop, Object object) { try { Invoker method = metaClass.getGetInvoker(prop.getName()); try { return method.invoke(object, NO_ARGUMENTS); } catch (Throwable t) { throw ExceptionUtil.unwrapThrowable(t); }} catch (RuntimeException e) {// This is a run-time exception. } catch (Throwable t) { throw new ReflectionException("Could not get property '" + prop.getName() + "' from " + object.getClass() + ". Cause: " + t.toString(), t); }}Copy the code