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Legal Studies如何在 MongoDB 中按标签获取文档？
你可以为此使用 $elemMatch 运算符。让我们创建一个包含文档的集合
> db.getDocumentsByTagsDemo.insertOne({"Tags":["Tag-1", "Tag-2", "Tag-3"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9eb4d5d628fa4220163b79")
}
> db.getDocumentsByTagsDemo.insertOne({"Tags":["Tag-2", "Tag-4", "Tag-5"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9eb4d5d628fa4220163b7a")
}
> db.getDocumentsByTagsDemo.insertOne({"Tags":["Tag-6", "Tag-4", "Tag-3"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9eb4d6d628fa4220163b7b")
}以下是使用 find() 方法从集合中显示所有文档的查询
> db.getDocumentsByTagsDemo.find().pretty();
这将生成以下输出
{
"_id" : ObjectId("5c9eb4d5d628fa4220163b79"),
"Tags" : [
"Tag-1",
"Tag-2",
"Tag-3"
]
}
{
"_id" : ObjectId("5c9eb4d5d628fa4220163b7a"),
"Tags" : [
"Tag-2",
"Tag-4",
"Tag-5"
]
}
{
"_id" : ObjectId("5c9eb4d6d628fa4220163b7b"),
"Tags" : [
"Tag-6",
"Tag-4",
"Tag-3"
]
}以下是按标签获取文档的查询
> db.getDocumentsByTagsDemo.find({Tags: { $elemMatch: { $eq: "Tag-2" } }}).pretty();这将生成以下输出
{
"_id" : ObjectId("5c9eb4d5d628fa4220163b79"),
"Tags" : [
"Tag-1",
"Tag-2",
"Tag-3"
]
}
{
"_id" : ObjectId("5c9eb4d5d628fa4220163b7a"),
"Tags" : [
"Tag-2",
"Tag-4",
"Tag-5"
]
}以下是仅查找特定标签的查询
> db.getDocumentsByTagsDemo.find({Tags: "Tag-5"}).pretty();这将生成以下输出
{
"_id" : ObjectId("5c9eb4d5d628fa4220163b7a"),
"Tags" : [
"Tag-2",
"Tag-4",
"Tag-5"
]
}
更新于: 2019 年 7 月 30 日
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