免费网站空间有什么用,开网店需要多少资金,wordpress展开 折叠功能,南阳网站制作价格文章目录 1. $count 聚合阶段2. $skip 聚合阶段3. $project 聚合阶段1. 包含指定字段2. 排除_id字段3. 排除指定字段4. 不能同时指定包含字段和排除字段5. 排除嵌入式文档中的指定字段6. 包含嵌入式文档中的指定字段7. 添加新字段8. 重命名字段 1. $count 聚合阶段
计算匹配到… 文章目录 1. $count 聚合阶段2. $skip 聚合阶段3. $project 聚合阶段1. 包含指定字段2. 排除_id字段3. 排除指定字段4. 不能同时指定包含字段和排除字段5. 排除嵌入式文档中的指定字段6. 包含嵌入式文档中的指定字段7. 添加新字段8. 重命名字段 1. $count 聚合阶段
计算匹配到的文档数量
db.collection.aggregate([// 匹配条件{ $match: { field: value } },// 其他聚合阶段// ...// 计算匹配到的文档数量{ $count: total }
])首先使用 $match 阶段来筛选出满足条件的文档。然后可以添加其他的聚合阶段来进行进一步的数据处理。最后使用 $count 阶段来计算匹配到的文档数量并将结果存储在一个字段中在示例中是 “total”。
请注意$count 阶段只返回一个文档其中包含一个字段表示匹配到的文档数量。如果没有匹配到任何文档将返回一个文档该字段的值为 0。
构造测试数据
db.scores.drop()db.scores.insertMany([{ _id : 1, subject : History, score : 88 },{ _id : 2, subject : History, score : 92 },{ _id : 3, subject : History, score : 97 },{ _id : 4, subject : History, score : 71 },{ _id : 5, subject : History, score : 79 },{ _id : 6, subject : History, score : 83 }
])$match阶段筛选 score 大于 80 的文档并计算匹配到的文档数量
db.scores.aggregate([// 第一阶段{$match: {score: {$gt: 80}}},// 第二阶段{$count: passing_scores}]
){ passing_scores : 4 }SpringBoot整合MongoDB实现
// 输入文档实体类
Data
Document(collection scores)
public class Score {private int _id;private String subject;private int score;
}// 输出文档实体类
Data
public class AggregationResult {private String passing_scores;
}// 聚合操作
SpringBootTest
RunWith(SpringRunner.class)
public class BeanLoadServiceTest {Autowiredprivate MongoTemplate mongoTemplate;Testpublic void aggregateTest() {// $match 聚合阶段Criteria criteria Criteria.where(score).gt(80);MatchOperation match Aggregation.match(criteria);// $count 聚合阶段CountOperation count Aggregation.count().as(passing_scores);// 组合聚合阶段Aggregation aggregation Aggregation.newAggregation(match,count);// 执行聚合查询AggregationResultsAggregationResult results mongoTemplate.aggregate(aggregation, Score.class, AggregationResult.class);ListAggregationResult mappedResults results.getMappedResults();// 打印结果mappedResults.forEach(System.out::println);//AggregationResult(passing_scores4)}
}2. $skip 聚合阶段
$skip 用于跳过指定数量的文档并将剩余的文档传递给下一个聚合阶段。
{ $skip: num }构造测试数据
db.scores.drop()db.scores.insertMany([{ _id : 1, subject : History, score : 88 },{ _id : 2, subject : History, score : 92 },{ _id : 3, subject : History, score : 97 },{ _id : 4, subject : History, score : 71 },{ _id : 5, subject : History, score : 79 },{ _id : 6, subject : History, score : 83 }
])db.scores.aggregate([{ $skip : 3 }
]);// 1
{_id: 4,subject: History,score: 71
}// 2
{_id: 5,subject: History,score: 79
}// 3
{_id: 6,subject: History,score: 83
}$skip 跳过管道传递给它的前 3 个文档并将剩余的文档传递给下一个聚合阶段。
// 输入文档实体类
Data
Document(collection scores)
public class Score {private int _id;private String subject;private int score;
}// 输出文档实体类
Data
public class AggregationResult {private int _id;private String subject;private int score;
}// 聚合操作
SpringBootTest
RunWith(SpringRunner.class)
public class BeanLoadServiceTest {Autowiredprivate MongoTemplate mongoTemplate;Testpublic void aggregateTest() {// $skip 聚合阶段SkipOperation skip Aggregation.skip(3);// 组合聚合阶段Aggregation aggregation Aggregation.newAggregation(skip);// 执行聚合查询AggregationResultsAggregationResult results mongoTemplate.aggregate(aggregation, Score.class, AggregationResult.class);ListAggregationResult mappedResults results.getMappedResults();// 打印结果mappedResults.forEach(System.out::println);//AggregationResult(_id4, subjectHistory, score71)//AggregationResult(_id5, subjectHistory, score79)//AggregationResult(_id6, subjectHistory, score83)}
}3. $project 聚合阶段
将带所请求字段的文档传递至管道中的下个阶段。$project 返回的文档可以指定包含字段、排除 _id 字段、添加新字段以及计算现有字段的值。
$project 阶段具有以下原型形式
{ $project: { specification(s) } }1. 包含指定字段
默认情况下_id 字段包含在输出文档中。要在输出文档中包含输入文档中的任何其他字段必须在 $project指定如果您指定包含的字段在文档中并不存在那么 $project 将忽略该字段包含同时不会将该字段添加到文档中。
构造测试数据
db.books.drop()db.books.insertOne({_id : 1,title: abc123,isbn: 0001122223334,author: { last: zzz, first: aaa },copies: 5}
)以下 $project 阶段输出文档中仅包含 _id、title 和 author 字段
db.books.aggregate( [ { $project: { title: 1 , author: 1 } }
] ){_id: 1,title: abc123,author: {last: zzz,first: aaa}
}SpringBoot 整合 MongoDB实现
// 输入文档实体类
Data
Document(collection books)
public class Book {private int _id;private String title;private String isbn;private Author author;private int copies;Datapublic static class Author {private String last;private String first;}
}// 输出文档实体类
Data
public class AggregationResult {private int _id;private String title;private Author author;Datapublic static class Author {private String last;private String first;}
}// 聚合操作
SpringBootTest
RunWith(SpringRunner.class)
public class BeanLoadServiceTest {Autowiredprivate MongoTemplate mongoTemplate;Testpublic void testAggregate(){// project 阶段ProjectionOperation project Aggregation.project(title, author);// 组合阶段Aggregation aggregation Aggregation.newAggregation(project);// 执行聚合AggregationResultsAggregationResult aggregationResults mongoTemplate.aggregate(aggregation, Book.class, AggregationResult.class);ListAggregationResult mappedResults aggregationResults.getMappedResults();// 打印结果mappedResults.forEach(System.out::println);// AggregationResult(_id1, titleabc123, authorAggregationResult.Author(lastzzz, firstaaa))}
}2. 排除_id字段
构造测试数据
db.books.drop()db.books.insertOne({_id : 1,title: abc123,isbn: 0001122223334,author: { last: zzz, first: aaa },copies: 5}
)以下 $project 阶段输出文档中仅包含 title 和 author 字段
db.books.aggregate( [ { $project: { _id: 0, title: 1, author: 1 } }
] ){title: abc123,author: {last: zzz,first: aaa}
}SpringBoot 整合 MongoDB实现
// 输入文档实体类
Data
Document(collection books)
public class Book {private int _id;private String title;private String isbn;private Author author;private int copies;Datapublic static class Author {private String last;private String first;}
}// 输出文档实体类
Data
public class AggregationResult {private int _id;private String title;private String isbn;private Author author;private int copies;Datapublic static class Author {private String last;private String first;}
}// 聚合操作
SpringBootTest
RunWith(SpringRunner.class)
public class BeanLoadServiceTest {Autowiredprivate MongoTemplate mongoTemplate;Testpublic void testAggregate(){// project 阶段ProjectionOperation project Aggregation.project(title, author).andExclude(_id);// 组合阶段Aggregation aggregation Aggregation.newAggregation(project);// 执行聚合AggregationResultsAggregationResult aggregationResults mongoTemplate.aggregate(aggregation, Book.class, AggregationResult.class);ListAggregationResult mappedResults aggregationResults.getMappedResults();// 打印结果mappedResults.forEach(System.out::println);// AggregationResult(titleabc123, authorAggregationResult.Author(lastzzz, firstaaa))}
}3. 排除指定字段
构造测试数据
db.books.drop()db.books.insertOne({_id : 1,title: abc123,isbn: 0001122223334,author: { last: zzz, first: aaa },copies: 5,lastModified: 2016-07-28}
)在 $project 阶段中输出文档排除 title 和 isbn 字段
db.books.aggregate( [ { $project: { title: 0, isbn: 0 } }
] )// 1
{_id: 1,author: {last: zzz,first: aaa},copies: 5,lastModified: 2016-07-28
}SpringBoot 整合 MongoDB实现
SpringBootTest
RunWith(SpringRunner.class)
public class BeanLoadServiceTest {Autowiredprivate MongoTemplate mongoTemplate;Testpublic void testAggregate(){// project 阶段ProjectionOperation project Aggregation.project().andExclude(isbn,title);// 组合阶段Aggregation aggregation Aggregation.newAggregation(project);// 执行聚合AggregationResultsAggregationResult aggregationResults mongoTemplate.aggregate(aggregation, Book.class, AggregationResult.class);ListAggregationResult mappedResults aggregationResults.getMappedResults();// 打印结果mappedResults.forEach(System.out::println);// AggregationResult(_id1, titlenull, isbnnull, authorAggregationResult.Author(lastzzz, firstaaa), copies5, lastModified2016-07-28)}
}4. 不能同时指定包含字段和排除字段
构造测试数据
db.books.drop()db.books.insertOne({_id : 1,title: abc123,isbn: 0001122223334,author: { last: zzz, first: aaa },copies: 5,lastModified: 2016-07-28}
)在 $project 阶段中输出文档排除 title 和 isbn 字段
db.books.aggregate( [ { $project: { title: 0, isbn: 1 } }
] )报错信息
[Error] Bad projection specification, cannot include fields or add computed fields during an exclusion projection: { title: 0.0, isbn: 1.0 }
原因分析在投影规范中除_id字段外不要在包含投影规范中使用排除操作。下面这样是可以的
db.books.aggregate( [ { $project: { _id: 0, isbn: 1 } }
] )5. 排除嵌入式文档中的指定字段
构造测试数据
db.books.drop()db.books.insertOne({_id : 1,title: abc123,isbn: 0001122223334,author: { last: zzz, first: aaa },copies: 5,lastModified: 2016-07-28}
)以下 $project 阶段中输出文档排除 author.first 和 lastModified 字段
db.books.aggregate( [ { $project: { author.first: 0, lastModified: 0 } }
] ){_id: 1,title: abc123,isbn: 0001122223334,author: {last: zzz},copies: 5
}6. 包含嵌入式文档中的指定字段
构造测试数据
db.books.drop()db.books.insertMany([{ _id: 1, user: 1234, stop: { title: book1, author: xyz, page: 32 } },{_id: 2, user: 7890, stop: [ { title: book2, author: abc, page: 5 }, { title: book3, author: ijk, page: 100 } ] }]
)以下 $project 阶段仅包含嵌入式文档中的 title 字段
db.books.aggregate( [ { $project: { stop.title: 1 } }
] )// 1
{_id: 1,stop: {title: book1}
}// 2
{_id: 2,stop: [{title: book2},{title: book3}]
}7. 添加新字段
构造测试数据
db.books.drop()db.books.insertOne({_id : 1,title: abc123,isbn: 0001122223334,author: { last: zzz, first: aaa },copies: 5}
)以下 $project 阶段添加新字段 isbn、lastName 和 copiesSold
db.books.aggregate([{$project: {title: 1,isbn: {prefix: { $substr: [ $isbn, 0, 3 ] },group: { $substr: [ $isbn, 3, 2 ] },publisher: { $substr: [ $isbn, 5, 4 ] },title: { $substr: [ $isbn, 9, 3 ] },checkDigit: { $substr: [ $isbn, 12, 1] }},lastName: $author.last,copiesSold: $copies}}]
){_id: 1,title: abc123,isbn: {prefix: 000,group: 11,publisher: 2222,title: 333,checkDigit: 4},lastName: zzz,copiesSold: 5
}8. 重命名字段
构造测试数据
db.books.drop()db.books.insertOne({_id : 1,title: abc123,isbn: 0001122223334,author: { last: zzz, first: aaa },copies: 5}
)以下 $project 阶段将字段 copies重命名为 copiesSold
db.books.aggregate([{$project: {title: 1,copiesSold: $copies}}]
){_id: 1,title: abc123,copiesSold: 5
}SpringBoot 整合MongoDB实现
// 输入文档
Data
Document(collection books)
public class Book {private int _id;private String title;private String isbn;private Author author;private int copies;private String lastModified;Datapublic static class Author {private String last;private String first;}
}// 输出文档
Data
public class AggregationResult {private int _id;private String title;private String isbn;private Author author;private int copiesSold;private String lastModified;Datapublic static class Author {private String last;private String first;}
}// 聚合操作
SpringBootTest
RunWith(SpringRunner.class)
public class BeanLoadServiceTest {Autowiredprivate MongoTemplate mongoTemplate;Testpublic void testAggregate(){// project 阶段ProjectionOperation project Aggregation.project(title).and(copies).as(copiesSold);// 组合阶段Aggregation aggregation Aggregation.newAggregation(project);// 执行聚合AggregationResultsAggregationResult aggregationResults mongoTemplate.aggregate(aggregation, Book.class, AggregationResult.class);ListAggregationResult mappedResults aggregationResults.getMappedResults();// 打印结果mappedResults.forEach(System.out::println);// AggregationResult(_id1, titleabc123, isbnnull, authornull, copiesSold5, lastModifiednull)}
}
