首先让我们创建一个包含文档的集合-
> db.projectionAnElementDemo.insertOne( ... { ... "CustomerId":100, ... "CustomerDetails": [ ... { ... "CustomerName": "Chris", ... "CustomerCountryName": "US" ... }, ... { ... "CustomerName": "Robert", ... "CustomerCountryName": "UK" ... } ... ] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5cd31c56b64f4b851c3a13ea") }
以下是在find()
方法的帮助下显示集合中所有文档的查询-
> db.projectionAnElementDemo.find().pretty();
这将产生以下输出-
{ "_id" : ObjectId("5cd31c56b64f4b851c3a13ea"), "CustomerId" : 100, "CustomerDetails" : [ { "CustomerName" : "Chris", "CustomerCountryName" : "US" }, { "CustomerName" : "Robert", "CustomerCountryName" : "UK" } ] }
以下是对数组字段中的项目元素的查询-
> db.projectionAnElementDemo.find({},{CustomerId:1, "CustomerDetails.CustomerName":1}).pretty();
这将产生以下输出-
{ "_id" : ObjectId("5cd31c56b64f4b851c3a13ea"), "CustomerId" : 100, "CustomerDetails" : [ { "CustomerName" : "Chris" }, { "CustomerName" : "Robert" } ] }