MyBatis“或”标准

Question

I want to create a query with MyBatis, which will produce something like:

SELECT first_field, second_filed, third_field
WHERE first_field > 1 AND (second_field > 0 OR third_field < 0)

How could I construct that with Criteria objects?

Answer 1

One way to do this would be to extend the generated Example classes :

The generated "example" class includes a nested inner class where the actual functionality of the predicates exists. This inner class is always named GeneratedCriteria.

MBG also generates an inner class named Criteria which extends GeneratedCriteria and which you may use for adding your own functions to the example classes. The Criteria class will not be deleted by the Eclipse Java code merger, so you may add to it without fear of losing your changes upon regeneration.

So basically,generate your example class, and add your custom criteria.

    public Criteria multiColumnOrClause(String value1, String value2) {
        addCriterion("value1 = " + value1 + " OR value2 = " + value2);
        return this;
    }

If you reuse it often, and don't want to do this for all your mappers, you can also extract the logic in a "plugin", although the documentation is a bit lacking on this, there's only one example :

org.mybatis.generator.plugins.CaseInsensitiveLikePlugin

Answer 2

Since a AND (b OR c) is the same as (a AND b) or (a AND c)

TestTableExample example = new TestTableExample();
example.createCriteria()
  .andField1GreaterThan(1)
  .andField2GreaterThan(0);
example.or(example.createCriteria()
  .andField1GreaterThan(1)
  .andField3LessThan(0));

then sit back and let the SQL optimizer figure it out.

Answer 3

据我所知，使用标准生成的映射器是不可能的。