MongoDB集合中项目特定的数组字段？
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"
}
]
}