Spring-Data-MongoDB中MongoTemplate的使用

本文主要是介绍Spring-Data-MongoDB中MongoTemplate的使用，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

find
- mongoTemplate.find(Query query, Class<T> entityClass )
  - 返回值 List<T>
  - 实例:List<User> users = mongoTemplate.find(new Query(Criteria.where("age").is(20).and("username").is("zhangsan")), User.class);
- mongoTemplate.find(Query query, Class<T> entityClass,String Collectionname )
  - 返回值 List<T>
  - 实例:List<User> users1 = mongoTemplate.find(new Query(Criteria.where("age").is(20).and("username").is("zhangsan1")), User.class, "user");
- mongoTemplate.findAll(Class<T> entityClass)
  - 返回值:List<T>
  - 实例:List<User> all = mongoTemplate.findAll(User.class);
- 代码示例:
- mongoTemplate.findAll(Class<T> entityClass,String Collectionname)
  - 返回值:List<T>
  - 实例:List<User> all = mongoTemplate.findAll(User.class,"user");
Aggregation
- Aggregation.project(String... fields)
  - 返回值:ProjectionOperation
  - 实例：ProjectionOperation project = Aggregation.project("age", "username");
- Aggregation.match（Criteria criteria）
  - 返回值：MatchOperation
  - 实例：MatchOperation match = Aggregation.match( Criteria().where("age").is(20));
- Aggregation.group（String... fields ）
  - 返回值：GroupOperation
  - 实例：GroupOperation group = Aggregation.group("username","age").sum("age").as("count");
- 代码示例：多字段分组
- 代码示例：单字段分组求和
- 代码示例：多字段分组求和
  - Aggregation.limit(long maxElements)
    - 返回值：LimitOperation
    - 实例：LimitOperation limit = Aggregation.limit(2);
    - 注释：只查询集合中的几个文档
  - Aggregation.sortByCount(String field)
    - 返回值:SortByCountOperation
    - 实例:SortByCountOperation sort = Aggregation.sortByCount("age");
    - 注释:查询结果会按照age排序,并计算每个age的个数.
  - 代码示例:
  - Aggregation.skip(long maxElements)
    - 返回值:SkipOperation
    - 实例:SkipOperation skip = Aggregation.skip((long)2);
    - 注释：跳过集合中前几个文档。
  - Aggregation.sort(Direction direction, String... fields);
    - 返回值：SortOperation
    - 实例：SortOperation sort = Aggregation.sort(Sort.Direction.DESC, "age");
- 代码示例:
  - Aggregation.unwind(String field)
    - 返回值:UnwindOperation
    - 实例:UnwindOperation unwind = Aggregation.unwind("sizes");
    - 注释:会查询出只有该字段的数据.
  - 代码示例:
  - Aggregation.newAggregation(Class<T> type, AggregationOperation... operations)
    - 返回值: TypedAggregation<T>
    - 实例:TypedAggregation<User> userTypedAggregation = Aggregation.newAggregation(User.class, skip,sort);
    - 注释:将Aggregation各个条件进行组合.交由mongoTemplate进行处理.
  - mongoTemplate.aggregate(TypedAggregation<?> aggregation, String inputCollectionName, Class<O> outputType);
    - 返回值:AggregationResults<Document>
    - 实例:AggregationResults<Document> user = mongoTemplate.aggregate(userTypedAggregation, "user", Document.class);
count
- mongoTemplate.count(Query query, Class<?> entityClass);
  - 返回值:long
  - 实例:long count = mongoTemplate.count(new Query(Criteria.where("age").is(20)), User.class);