检查 MongoDB 文档中某个字段是否存在值?
mongodbdatabasebig data analytics更新于 2026/1/15 16:37:17
要检查 MongoDB 文档中某个字段是否存在值，可以使用 find() 和 $exists 运算符。首先，我们创建一个包含文档的集合。 −
> db.checkIfValueDemo.insertOne({"PlayerName":"John Smith","PlayerScores":[5000,98595858,554343]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cc6f507af8e7a4ca6b2ad98")
}
> db.checkIfValueDemo.insertOne({"PlayerName":"John Doe","PlayerScores":[]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cc6f512af8e7a4ca6b2ad99")
}
> db.checkIfValueDemo.insertOne({"PlayerName":"Carol Taylor","PlayerScores":[7848474,8746345353]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cc6f521af8e7a4ca6b2ad9a")
}
> db.checkIfValueDemo.insertOne({"PlayerName":"David Miller","PlayerScores":[]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cc6f531af8e7a4ca6b2ad9b")
}
以下是使用 find() 方法显示集合中的所有文档的查询 −
> db.checkIfValueDemo.find().pretty();
这将产生以下输出 −
{
"_id" : ObjectId("5cc6f507af8e7a4ca6b2ad98"),
"PlayerName" : "John Smith",
"PlayerScores" : [
5000,
98595858,
554343
]
}
{
"_id" : ObjectId("5cc6f512af8e7a4ca6b2ad99"),
"PlayerName" : "John Doe",
"PlayerScores" : [ ]
}
{
"_id" : ObjectId("5cc6f521af8e7a4ca6b2ad9a"),
"PlayerName" : "Carol Taylor",
"PlayerScores" : [
7848474,
8746345353
]
}
{
"_id" : ObjectId("5cc6f531af8e7a4ca6b2ad9b"),
"PlayerName" : "David Miller",
"PlayerScores" : [ ]
}
以下查询用于检查文档中某个字段是否存在值。这里，我们检查字段"PlayerScores"的值为[ ] −
> db.checkIfValueDemo.find({'PlayerScores.0' : {$exists: true}}).count();
这将产生以下输出 −
2
