!273 feat(QueryWrapper and Wrappers): add Wrappers.query(entityClass)

Merge pull request !273 from 阿超/3.0

mybatis-plus-core/src/main/java/com/baomidou/mybatisplus/core/conditions/query/QueryWrapper.java

@@ -46,7 +46,7 @@ public class QueryWrapper<T> extends AbstractWrapper<T, String, QueryWrapper<T>>
     private final SharedString sqlSelect = new SharedString();
 
     public QueryWrapper() {
-        this(null);
+        this((T) null);
     }
 
     public QueryWrapper(T entity) {
@@ -54,6 +54,11 @@ public class QueryWrapper<T> extends AbstractWrapper<T, String, QueryWrapper<T>>
         super.initNeed();
     }
 
+    public QueryWrapper(Class<T> entityClass) {
+        super.setEntityClass(entityClass);
+        super.initNeed();
+    }
+
     public QueryWrapper(T entity, String... columns) {
         super.setEntity(entity);
         super.initNeed();

mybatis-plus-core/src/main/java/com/baomidou/mybatisplus/core/toolkit/Wrappers.java

@@ -61,6 +61,17 @@ public final class Wrappers {
         return new QueryWrapper<>(entity);
     }
 
+    /**
+     * 获取 QueryWrapper&lt;T&gt;
+     *
+     * @param entityClass 实体类class
+     * @param <T>    实体类泛型
+     * @return QueryWrapper&lt;T&gt;
+     */
+    public static <T> QueryWrapper<T> query(Class<T> entityClass) {
+        return new QueryWrapper<>(entityClass);
+    }
+
     /**
      * 获取 LambdaQueryWrapper&lt;T&gt;
      *