Query an Array of Embedded Documents查询嵌入文档的数组

Specify a Query Condition on a Field Embedded in an Array of Documents对嵌入在文档数组中的字段指定查询条件

If you do not know the index position of the document nested in the array, concatenate the name of the array field, with a dot (.) and the name of the field in the nested document.如果您不知道嵌套在数组中的文档的索引位置，请用句点（.）连接数组字段的名称和嵌套文档中字段的名称。

The following example selects all documents where the instock array has at least one embedded document that contains the field qty whose value is less than or equal to 20:以下示例选择instock数组至少有一个嵌入文档的所有文档，该文档包含值小于或等于20的字段qty：

const cursor = db.collection('inventory').find({
  'instock.qty': { $lte: 20 }
});

Use the Array Index to Query for a Field in the Embedded Document使用数组索引查询嵌入文档中的字段

Using dot notation, you can specify query conditions for field in a document at a particular index or position of the array. The array uses zero-based indexing.使用点表示法，可以为文档中位于数组特定索引或位置的字段指定查询条件。数组使用基于零的索引。

The following example selects all documents where the instock array has as its first element a document that contains the field qty whose value is less than or equal to 20:以下示例选择instock数组的第一个元素为文档的所有文档，该文档包含值小于或等于20的字段qty：

const cursor = db.collection('inventory').find({
  'instock.0.qty': { $lte: 20 }
});

A Single Nested Document Meets Multiple Query Conditions on Nested Fields单个嵌套文档在嵌套字段上满足多个查询条件

Use $elemMatch operator to specify multiple criteria on an array of embedded documents such that at least one embedded document satisfies all the specified criteria.使用$elemMatch运算符在嵌入文档数组中指定多个条件，以便至少有一个嵌入文档满足所有指定的条件。

The following example queries for documents where the instock array has at least one embedded document that contains both the field qty equal to 5 and the field warehouse equal to A:以下示例查询instock数组至少有一个嵌入文档的文档，该文档包含等于5的字段qty和等于A的字段warehouse：

const cursor = db.collection('inventory').find({
  instock: { $elemMatch: { qty: 5, warehouse: 'A' } }
});

The following example queries for documents where the instock array has at least one embedded document that contains the field qty that is greater than 10 and less than or equal to 20:以下示例查询instock数组至少有一个嵌入文档的文档，该文档包含大于10且小于或等于20的字段qty：

const cursor = db.collection('inventory').find({
  instock: { $elemMatch: { qty: { $gt: 10, $lte: 20 } } }
});

Combination of Elements Satisfies the Criteria元素组合符合标准

If the compound query conditions on an array field do not use the $elemMatch operator, the query selects those documents whose array contains any combination of elements that satisfies the conditions.如果数组字段上的复合查询条件不使用$elemMatch运算符，则查询将选择其数组包含满足条件的任何元素组合的文档。

For example, the following query matches documents where any document nested in the instock array has the qty field greater than 10 and any document (but not necessarily the same embedded document) in the array has the qty field less than or equal to 20:例如，以下查询匹配嵌套在instock数组中的任何文档的qty字段大于10，并且数组中的任意文档（但不一定是同一嵌入文档）的qty字段小于或等于20的文档：

const cursor = db.collection('inventory').find({
  'instock.qty': { $gt: 10, $lte: 20 }
});

The following example queries for documents where the instock array has at least one embedded document that contains the field qty equal to 5 and at least one embedded document (but not necessarily the same embedded document) that contains the field warehouse equal to A:以下示例查询instock数组至少有一个包含等于5的字段qty的嵌入文档和至少一个包含相等于A的字段warehouse的嵌入文档（但不一定是同一嵌入文档）的文档：

const cursor = db.collection('inventory').find({
  'instock.qty': 5,
  'instock.warehouse': 'A'
});