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Query

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LambdaTemplate supports multiple result forms:

  • List: map results to a list of objects.
  • Object: map a single result.
  • Count: rewrite the query to COUNT using dialect support.
  • Streaming: handle results via RowCallbackHandler or ResultSetExtractor.
  • Pagination: paginate queries.
Tip

For building conditions used in queries, see where builder.

Query list​

Run a query and map results to a list.

Map to entity type
LambdaTemplate lambda = ...;

List<User> result = null;
result = lambda.query(User.class)
               .le(User::getId, 100)   // match id <= 100
               .queryForList();        // map to entity type
Map to a specific type
LambdaTemplate lambda = ...;

List<UserVO> result = null;
result = lambda.query(User.class)
               .le(User::getId, 100)        // match id <= 100
               .queryForList(UserVO.class); // map to target type
  • When mapping User results to another type, mapping follows the target type’s rules. See Object Mapping for details.
Map to Map
LambdaTemplate lambda = ...;

List<Map<String,Object>> result = null;
result = lambda.query(User.class)
               .le(User::getId, 100)    // match id <= 100
               .queryForMapList();      // map to Map
  • Map keys correspond to User property names.
LambdaTemplate lambda = ...;
RowMapper<UserVO> rowMapper = new BeanMappingRowMapper(UserVO.class);

List<UserVO> result = null;
result = lambda.query(User.class)
               .le(User::getId, 100)    // match id <= 100
               .queryForList(rowMapper);// use RowMapper for mapping
  • Use RowMapper to customize row mapping from ResultSet.

Query a single object​

Run a query and map the single result; multiple matches throw an exception.

Map to entity type
LambdaTemplate lambda = ...;

User result = null;
result = lambda.query(User.class)
               .eq(User::getId, 100)   // match id = 100
               .queryForObject();      // map to entity type
Map to a specific type
LambdaTemplate lambda = ...;

UserVO result = null;
result = lambda.query(User.class)
               .eq(User::getId, 100)          // match id = 100
               .queryForObject(UserVO.class); // map to target type
  • When mapping User results to another type, mapping follows the target type’s rules. See Object Mapping for details.
Map to Map
LambdaTemplate lambda = ...;

Map<String,Object> result = null;
result = lambda.query(User.class)
               .eq(User::getId, 100) // match id = 100
               .queryForMap();       // map to Map
  • Map keys correspond to User property names.
LambdaTemplate lambda = ...;
RowMapper<UserVO> rowMapper = new BeanMappingRowMapper(UserVO.class);

List<UserVO> result = null;
result = lambda.query(User.class)
               .le(User::getId, 100)     // match id <= 100
               .queryForObject(rowMapper);// use RowMapper for mapping
  • Use RowMapper to customize row mapping from ResultSet.

Count​

dbVisitor rewrites the query into a COUNT using dialect support. Example:

-- original query
select id, name from users where id <= 100;
-- rewritten as count query
select count(*) from (select id, name from users where id <= 100;) as TEMP_T;
LambdaTemplate lambda = ...;
RowMapper<UserVO> rowMapper = new BeanMappingRowMapper(UserVO.class);

int count = lambda.query(User.class)
                  .le(User::getId, 100)  // match id <= 100
                  .queryForCount();      // count as int
                //.queryForLargeCount(); // count as long
  • Choose queryForCount or queryForLargeCount based on size needs.

Streaming​

Use RowCallbackHandler to process each row without collecting the result set.

RowCallbackHandler handler = new RowCallbackHandler() {
    @Override
    public void processRow(ResultSet rs, int rowNum) throws SQLException {
        ...
    }
};

LambdaTemplate lambda = ...;

lambda.query(User.class)
      .eq(User::getId, 100)  // match id = 100
      .query(handler);       // process via RowCallbackHandler

Use ResultSetExtractor to process the entire ResultSet.

ResultSetExtractor extractor = new ResultSetExtractor<Map<Integer, String>>() {
    public Map<Integer, String> extractData(ResultSet rs) throws SQLException {
        Map<Integer, String> hashMap = new HashMap<>();

        while (rs.next()) {
            int id = rs.getInt("id");
            String name = rs.getString("name");
            hashMap.put(id, name);
        }

        return hashMap;
    }
};

LambdaTemplate lambda = ...;

Map<Integer, String> result = null;
result = lambda.query(User.class)
               .eq(User::getId, 100)  // match id = 100
               .query(extractor);     // process via ResultSetExtractor

Pagination​

Tip

Pagination depends on dialect support; see database support for supported databases.

dbVisitor provides built-in pagination with no extra config. Usage:

Using page arguments
LambdaTemplate lambda = ...;

List<User> result = null;
result = lambda.query(User.class)
               .usePage(pageInfo)
               .le(User::getId, 100) // match id <= 100
               .initPage(10, 1)      // page size 10, fetch page 2 (0-based)
               .queryForList();      // paged query
Using a Page object
LambdaTemplate lambda = ...;

// Page object
Page page = new PageObject();
page.setPageNumberOffset(1); // start page numbering at 1
page.setPageSize(10);        // 10 rows per page
page.setCurrentPage(2);      // fetch page 2

// paged query
List<User> result = null;
result = lambda.query(User.class)
               .le(User::getId, 100) // match id <= 100
               .usePage(page)        // pagination info
               .queryForList();      // paged query
  • The Page object has more helpers; see Page object.
  • The list and result-processing methods above can be combined with pagination.