删除MongoDB中数组字段中的所有元素？
您可以为此使用$set运算符。语法如下-
db.yourCollectionName.update({}, { $set : {"yourFieldName": [] }} , {multi:true} );为了理解上述语法，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.deleteAllElementsInArrayDemo.insertOne({"InstructorName":"Larry","InstructorTechnicalSubject":["Java","MongoDB"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8fb971d3c9d04998abf00e")
}
> db.deleteAllElementsInArrayDemo.insertOne({"InstructorName":"Mike","InstructorTechnicalSubject":["C","C++","Python"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8fb98ad3c9d04998abf00f")
}在find()method的帮助下显示集合中的所有文档。查询如下-
> db.deleteAllElementsInArrayDemo.find().pretty();
以下是输出-
{
"_id" : ObjectId("5c8fb971d3c9d04998abf00e"),
"InstructorName" : "Larry",
"InstructorTechnicalSubject" : [
"Java",
"MongoDB"
]
}
{
"_id" : ObjectId("5c8fb98ad3c9d04998abf00f"),
"InstructorName" : "Mike",
"InstructorTechnicalSubject" : [
"C",
"C++",
"Python"
]
}这是删除数组字段中所有元素的查询-
> db.deleteAllElementsInArrayDemo.update({}, { $set : {"InstructorTechnicalSubject": [] }} , {multi:true} );
WriteResult({ "nMatched" : 2, "nUpserted" : 0, "nModified" : 2 })现在让我们使用来检查集合中的所有文档find()。查询如下-
> db.deleteAllElementsInArrayDemo.find().pretty();
以下是输出。我们删除了“InstructorTechnicalSubject”数组字段的所有元素：
{
"_id" : ObjectId("5c8fb971d3c9d04998abf00e"),
"InstructorName" : "Larry",
"InstructorTechnicalSubject" : [ ]
}
{
"_id" : ObjectId("5c8fb98ad3c9d04998abf00f"),
"InstructorName" : "Mike",
"InstructorTechnicalSubject" : [ ]
}