是否可以使用MongoDB查询数组对象中字段中具有特定值的条目？
是的，要使用MongoDB查询数组对象中的字段，请使用以下语法-
db.yourCollectionName.find({"yourOuterFieldName": { $elemMatch: { "yourInnerFieldName": "yourValue" } } } ).pretty();为了理解上述概念，让我们用文档创建一个集合。使用文档创建集合的查询如下-
> db.objectInAnArrayDemo.insertOne({ "StudentDetails": [{
"StudentName": "John", "StudentMessage": "Hi"}, {"StudentName": "Larry", "StudentMessage": "Hello"}]})
{
"acknowledged" : true,
"insertedId" : ObjectId("5c92635d36de59bd9de06381")
}
> db.objectInAnArrayDemo.insertOne({ "StudentDetails": [{
"StudentName": "Carol", "StudentMessage": "Hello"}, {"StudentName": "David", "StudentMessage": "Good Morning"}]})
{
"acknowledged" : true,
"insertedId" : ObjectId("5c92637936de59bd9de06382")
}在find()方法的帮助下显示集合中的所有文档。查询如下-
> db.objectInAnArrayDemo.find().pretty();
以下是输出-
{
"_id" : ObjectId("5c92635d36de59bd9de06381"),
"StudentDetails" : [
{
"StudentName" : "John",
"StudentMessage" : "Hi"
},
{
"StudentName" : "Larry",
"StudentMessage" : "Hello"
}
]
}
{
"_id" : ObjectId("5c92637936de59bd9de06382"),
"StudentDetails" : [
{
"StudentName" : "Carol",
"StudentMessage" : "Hello"
},
{
"StudentName" : "David",
"StudentMessage" : "Good Morning"
}
]
}这是使用MongoDB查询数组对象中字段的信息-
> db.objectInAnArrayDemo.find({"StudentDetails": { $elemMatch: { "StudentMessage": "Good Morning" } } } ).pretty();以下是输出-
{
"_id" : ObjectId("5c92637936de59bd9de06382"),
"StudentDetails" : [
{
"StudentName" : "Carol",
"StudentMessage" : "Hello"
},
{
"StudentName" : "David",
"StudentMessage" : "Good Morning"
}
]
}