Ibatis/MyBatis動態選擇，無需創建任何Pojo/Mapper

Question

是否有任何方法使用Ibatis/MyBatis動態選擇/更新/刪除？

當我說「動態」時，這意味着我不想創建任何POJO/DataMapper。

任何URL示例都會受到歡迎。

Answer 1

是的，只需將resultType屬性設置爲map，表數據將被放置到列名的值的HashMap中。如果查詢返回多於一行，映射的行將被放入List中。如果你想選擇一個列，你可以得到這個值（如String，int等）或列表。

<select id="test1" resultType="map">select * from user</select> 
<select id="test2" resultType="map" parameterType="int"> 
    select * from user where id=#{value}</select> 
<select id="test3" resultType="string">select name from user</select> 
... 
// returns a list of maps 
List test = sqlSession.selectList("test1"); 

// returns a single map 
Object map = sqlSession.selectOne("test2", 0); 

// returns a list of strings 
List names = sqlSession.selectList("test3"); 

這適用於MyBatis 3;我認爲你可以在iBatis 2中做類似的事情。

Answer 2

是的，應該可以通過API在運行時構建映射，並使用Maps而不是實體類。

Answer 3

以下方法可能會有用。 說，你有一些通用的選擇界面，如：

public interface IAutoRepository { 
    /** 
    * The automatically generated insertPKs sql statements. 
    * Parts of the query can be set manually in the sql (insert-select query). 
    * 
    * @param items  the {@link WhereStmt} statements 
    * @return the inserted rows count 
    */ 
    @Transactional 
    <T extends WhereStmt> Integer insertPKs(@Param("items") List<T> items); 

    /** 
    * Returns the value based on the {@link Parameter} class 
    * 
    * @param param  the {@link Parameter} instance 
    * @return the searched value in a {@link java.util.Map} form 
    */ 
    @MapKey("VAL") 
    <T extends Parameter> Map<String, Map<String, ?>> getDistinctValues(@Param("param") T param); 
} 

據一些外部類型（比如，單柱或日期範圍或任何範圍），你可以在模板Common.xml定義以下查詢：

<sql id="includeDistinctValues"> 
SELECT 
    <choose> 
     <when test='param.type.name() == "set"'> 
      DISTINCT ${param.column} AS val 
     </when> 
     <when test='param.type.name() == "date" or param.type.name() == "range"'> 
      <some uid>    AS val, 
      MIN(${param.minColumn}) AS min, 
      MAX(${param.maxColumn}) AS max 
     </when> 
    </choose> 
FROM ${entityTable} 
</sql> 

從mybatis收到的是java.util.Map。然後，你就可以使用它的一些實物，如：

public enum StmtType { 
    set((valMap) -> { 
     final Set<String> distinctValues = valMap 
       .values() 
       .stream() 
       .map(val -> (String) val.get("VAL")) 
       //use in date/range case 
       //final Date minDate = (Date) val.get("MIN"); 
       //final Date maxDate = (Date) val.get("MAX"); 
       .collect(Collectors.toSet()); 
     return distinctValues; 
    }, 
      (values, params) -> { 
       final SetParameter parameter = (SetParameter) params.getParams(); 
       return new WhereSetStmt<>(parameter.getColumn(), values, params.getIncludeEmptyValues()); 
      }); 
    @Getter 
    private Function<Map<String, Map<String, ?>>, ? extends Iterable> toValue; 
    @Getter 
    private BiFunction<Collection, DataParam, ? extends WhereStmt> toWhereStmt; 

    StmtType(
      Function<Map<String, Map<String, ?>>, ? extends Iterable> toValue, 
      BiFunction<Collection, DataParam, ? extends WhereStmt> toWhereStmt 
    ) { 
     this.toValue = toValue; 
     this.toWhereStmt = toWhereStmt; 
    } 
} 

其中的setParameter可以表示爲以下幾點：

@Getter 
public class SetParameter extends Parameter { 
    /** 
    * Column in sql query, 
    */ 
    private final String column; 
    public SetParameter(String column) { 
     super(StmtType.set); 
     this.column = column; 
    } 
} 

此外，你可以定義一些WhereStmt像：

public abstract class WhereStmt { 
    /** 
    * Type of the statement 
    */ 
    private final StmtType type; 
    /** 
    * Shall empty values be included. 
    */ 
    private final boolean includeEmptyValues; 
} 

@Getter 
public class WhereSetStmt<T> extends WhereStmt { 
    /** 
    * The column for `column` IN (...) statement 
    */ 
    private String column; 
    /** 
    * Values for `column` IN (...) statement 
    */ 
    private Collection<T> values; 

    public WhereSetStmt(String column, Collection<T> values, boolean includeEmptyValues) { 
     super(StmtType.set, includeEmptyValues); 
     this.column = column; 
     this.values = values; 
    } 
} 

@Getter 
@AllArgsConstructor 
public final class DataParam<P extends Parameter> { 
    /** 
    * Whether to include nullable values. 
    */ 
    private final Boolean includeEmptyValues; 
    /** 
    * Represents database required information for later processing and sql statements generation. 
    */ 
    private final P params; 
} 

最後，在mybatis通用Common.xml您可以使用它像：

<sql id="includeInsertPkSelect"> 
    SELECT DISTINCT(${id}) 
    FROM ${entityTable} 
</sql> 

<sql id="includeInsertPkWhere"> 
    <if test="items != null and items.size() > 0"> 
     AND 
     <foreach collection="items" item="item" index="i" separator="AND"> 
      <choose> 
       <when test='item.type.name() == "set" and (item.values != null and item.values.size() > 0 or item.includeEmptyValues)'> 
        (
        <if test="item.values != null and item.values.size() > 0"> 
         ${item.column} IN 
         <foreach item="value" collection="item.values" separator="," open="(" 
           close=")"> 
          #{value} 
         </foreach> 
         <if test="item.includeEmptyValues"> 
          OR 
         </if> 
        </if> 
        <if test="item.includeEmptyValues"> 
         ${item.column} IS null 
        </if> 
        ) 
       </when> 

       <when test='item.type.name() == "date"'> 
        (
        COALESCE(${item.column}, SYSDATE + 1000000) 
        BETWEEN #{item.from} AND #{item.to} 
        <if test="item.includeEmptyValues"> 
         OR ${item.column} IS NULL 
        </if> 
        ) 
       </when> 
       <when test='item.type.name() == "range"'> 
        (
        COALESCE(${item.column}, 1000000000) 
        BETWEEN #{item.from} AND #{item.to} 
        <if test="item.includeEmptyValues"> 
         OR ${item.column} IS NULL 
        </if> 
        ) 
       </when> 
      </choose> 
     </foreach> 
    </if> 
</sql> 

，並結合SQL語句作爲模板，說：

<insert id='insertPKs'> 
    INSERT INTO requiredTable 
    <include refid="Common.includeInsertPkSelect"> 
     <property name="id" value="entityId"/> 
     <property name="entityTable" value="entityTable"/> 
    </include> 
    <include refid="Common.includeInsertPkWhere"> 
     <property name="id" value="entityId"/> 
     <property name="entityTable" value="entityTable"/> 
    </include> 
</insert>