MyBatis - 找不到构造函数

Question

I have a problem with MyBatis mapping. I have a domain class like this:

public class MyClass
{
   private Long id;
   private Date create;
   private String content;

   MyClass (Long id, Date create, String content)
   {
       this.id = id;
       this.create = create;
       this.content = content;
   }

   //getters and setters

A mapper class with a method like this:

   @Select("SELECT * FROM MyTable WHERE id=#{id}")
   MyClass getMyClass (@Param("id") Long id);

In the database the three columns are of type Number, Timestamp and Clob and have the same name as in the class fields.

When I use this method I get a: ExecutorException: No constructor found in [MyClass; matching [java.math.BigDecimal, java.sql.Timestamp, oracle.jdbc.OracleClob]

But if I remove the constructor from Myclass, then there is no problem at all . I would like to have the constructor, how can I fix it? I tried adding the @Results annotation in the mapper like so, but it didn't make any difference:

   @Results(value = {
      @Result(column = "id", property = "id", javaType = Long.class),
      @Result(column = "create", property = "create", javaType = Date.class),
      @Result(column = "content", property = "content", javaType = String.class)
   })

Answer 1

MyBatis expects your model objects to have a no-arguments constructor (and possibly setters for each mapped field). Add those and everything should work.

Answer 2

You can use the @ConstructorArgs instead as follows:

@ConstructorArgs({
    @Arg(column = "id", javaType = Long.class)
    ,@Arg(column = "create", javaType = Date.class)
    ,@Arg(column = "content", javaType = String.class)
})

Answer 3

Just completing the answer of @Kazuki Shimizu .

If you want to use the primitive type long instead of the wrapper Long in the constructor you need to change the binding to:

@ConstructorArgs({
   @Arg(column = "id", javaType = long.class)
   ,@Arg(column = "create", javaType = Date.class)
   ,@Arg(column = "content", javaType = String.class)
})

Answer 4

Mind that you need to add mybatis @Param annotation to the constructor in case you want to use @ConstructorArgs . So your constructor would look like:

public class MyClass
{
   private long id;
   private Date create;
   private String content;

   MyClass (@Param("id") long id, @Param("create") Date create, @Param("content") String content)
   {
       this.id = id;
       this.create = create;
       this.content = content;
   }

Then your mapper:

@ConstructorArgs({
   @Arg(name = "id", column = "id", javaType = long.class),
   @Arg(name = "create", column = "create", javaType = Date.class),
   @Arg(name = "content", column = "content", javaType = String.class)
})