MongoDB查詢文件
摘要：
MongoDB 查詢文件使用find()
方法。find()
方法以非結構化的方式來顯示所有文件。
db.collection.find()
語法
db.collection.find(...
MongoDB 查詢文件使用find()
方法。find()
方法以非結構化的方式來顯示所有文件。
db.collection.find( <query filter>, <projection> )
- query filter 查詢條件，指明返回哪些文件
- projection 查詢對映，指定查詢的文件要返回哪些欄位
<query filter>
為空的時候就是{},可以省略。所以db.collection.find()等價於db.collection.find({})
接著上一篇的實戰，我們先來看一下users集合現在還有哪一些文件
> db.users.find()
{ "_id" : ObjectId("5c77499137955b945af73220"), "name" : "tom", "age" : 20, "gender" : "male" }
{ "_id" : ObjectId("5c77499137955b945af73221"), "name" : "Linda", "age" : 18, "gender" : "female" }
{ "_id" : ObjectId("5c77731d37955b945af73222"), "name" : "Hanmeimei", "age" : 17, "gender" : "female" }
{ "_id" : ObjectId("5c7774b736397a1c0aa425ea"), "name" : "Jack", "age" : 28, "gender" : "male", "is_active" : 1 }
{ "_id" : ObjectId("5c7774b736397a1c0aa425eb"), "name" : "Lucy", "age" : 28, "gender" : "female", "is_active" : 1 }
下面我們通過命令來演示find()
方法的用法
1.查詢符合條件的文件
如:查詢age>25的全部文件
> db.users.find({"age": {$gt: 25}})
{ "_id" : ObjectId("5c7774b736397a1c0aa425ea"), "name" : "Jack", "age" : 28, "gender" : "male", "is_active" : 1 }
{ "_id" : ObjectId("5c7774b736397a1c0aa425eb"), "name" : "Lucy", "age" : 28, "gender" : "female", "is_active" : 1 }
2.查詢符合條件的文件的指定欄位
如:查詢age>25的人的name
> db.users.find({"age": {$gt: 25}}, {name:1})
{ "_id" : ObjectId("5c7774b736397a1c0aa425ea"), "name" : "Jack" }
{ "_id" : ObjectId("5c7774b736397a1c0aa425eb"), "name" : "Lucy" }
如我們所願返回了name
欄位，但是同時也返回了_id
欄位。_id
是預設返回的，如果不想要它返回許指定_id
：0
> db.users.find({"age": {$gt: 25}}, {name:1, _id:0})
{ "name" : "Jack" }
{ "name" : "Lucy" }
3.指定AND條件
如:查詢年齡大於25的男性
> db.users.find({"age": {$gt: 25}, "gender": "male"})
{ "_id" : ObjectId("5c7774b736397a1c0aa425ea"), "name" : "Jack", "age" : 28, "gender" : "male", "is_active" : 1 }
4.指定OR條件
如:查詢age=18的或者name是tom的文件
> db.users.find({$or: [{"name":"tom"}, {"age":18}]})
{ "_id" : ObjectId("5c77499137955b945af73220"), "name" : "tom", "age" : 20, "gender" : "male" }
{ "_id" : ObjectId("5c77499137955b945af73221"), "name" : "Linda", "age" : 18, "gender" : "female" }
5.指定AND和OR條件
如一下面的篩選滿足2個條件
- 年齡大於18
- 女性或者名字叫"Jack"
> db.users.find({"age":{$gt: 18}, $or:[{"gender":"female"}, {"name":"Jack"}]})
{ "_id" : ObjectId("5c7774b736397a1c0aa425ea"), "name" : "Jack", "age" : 28, "gender" : "male", "is_active" : 1 }
{ "_id" : ObjectId("5c7774b736397a1c0aa425eb"), "name" : "Lucy", "age" : 28, "gender" : "female", "is_active" : 1 }
如果某一個欄位對應的是陣列，我們可以修改數組裡面的某一個欄位嗎？
先給每一個文件插入一個欄位points，它對應的值是個陣列
> var points={[ { "points" : 85, "bonus" : 20 }, { "points" : 85, "bonus" : 10 } ]}
> db.users.updateMany({"age":{$gt:0}}, {$set:{"points":points}})
{ "acknowledged" : true, "matchedCount" : 5, "modifiedCount" : 5 }
> tmp=[{"points":90, "bonus":20}, {"points":88, "bonus":11}]
[
{
"points" : 90,
"bonus" : 20
},
{
"points" : 88,
"bonus" : 11
}
]
> db.users.update({"name": "tom"}, {$set: {"points": tmp}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 0 })
> db.users.find().pretty()
> db.users.find().pretty()
{
"_id" : ObjectId("5c77499137955b945af73220"),
"name" : "tom",
"age" : 20,
"gender" : "male",
"points" : [
{
"points" : 90,
"bonus" : 20
},
{
"points" : 88,
"bonus" : 11
}
]
}
{
"_id" : ObjectId("5c77499137955b945af73221"),
"name" : "Linda",
"age" : 18,
"gender" : "female",
"points" : [
{
"points" : 85,
"bonus" : 20
},
{
"points" : 85,
"bonus" : 10
}
]
}
{
"_id" : ObjectId("5c77731d37955b945af73222"),
"name" : "Hanmeimei",
"age" : 17,
"gender" : "female",
"points" : [
{
"points" : 85,
"bonus" : 20
},
{
"points" : 85,
"bonus" : 10
}
]
}
{
"_id" : ObjectId("5c7774b736397a1c0aa425ea"),
"name" : "Jack",
"age" : 28,
"gender" : "male",
"is_active" : 1,
"points" : [
{
"points" : 85,
"bonus" : 20
},
{
"points" : 85,
"bonus" : 10
}
]
}
{
"_id" : ObjectId("5c7774b736397a1c0aa425eb"),
"name" : "Lucy",
"age" : 28,
"gender" : "female",
"is_active" : 1,
"points" : [
{
"points" : 85,
"bonus" : 20
},
{
"points" : 85,
"bonus" : 10
}
]
}
這裡我想查詢points欄位裡面第一個points為90的
> db.users.find({"points.0.points": 90}).pretty()
{
"_id" : ObjectId("5c77499137955b945af73220"),
"name" : "tom",
"age" : 20,
"gender" : "male",
"points" : [
{
"points" : 90,
"bonus" : 20
},
{
"points" : 88,
"bonus" : 11
}
]
}
不指定陣列索引匹配欄位
> db.users.find({"points.bonus": 11}).pretty()
{
"_id" : ObjectId("5c77499137955b945af73220"),
"name" : "tom",
"age" : 20,
"gender" : "male",
"points" : [
{
"points" : 90,
"bonus" : 20
},
{
"points" : 88,
"bonus" : 11
}
]
}
只有points數組裡面的bonus滿足11就返回
還可以指定陣列文件的多個查詢條件，這裡我就不掩飾了
6.null
存在性篩選
> db.student.find()
{ "_id" : 1, "name" : "tom", "hobby" : null }
{ "_id" : 2, "name" : "Jack" }
> db.student.find({"hobby":null})
{ "_id" : 1, "name" : "tom", "hobby" : null }
{ "_id" : 2, "name" : "Jack" }
>
注意一下，我們篩選 hobby為null
的，沒有hobby這個欄位的夜篩選出來了
> db.student.find({"hobby":{$exists:false}})
{ "_id" : 2, "name" : "Jack" }
> db.student.find({"hobby":{$exists:true}})
{ "_id" : 1, "name" : "tom", "hobby" : null }
通過$exists
來指定
其他查詢文件的方法findOne()
看方法名就知道值查詢返回滿足條件的第一條記錄
> db.users.findOne({"age": {$gt: 20}})
{
"_id" : ObjectId("5c7774b736397a1c0aa425ea"),
"name" : "Jack",
"age" : 28,
"gender" : "male",
"is_active" : 1,
"points" : [
{
"points" : 85,
"bonus" : 20
},
{
"points" : 85,
"bonus" : 10
}
]
}