Mongodb array operation

1. Add an element to the end of the array

push Is that , If the specified key already exists , It adds an element to the end of an existing array , If not, a new array will be created

db.user.update({
    “_id” : ObjectId(“4ffcb2ed65282ea95f7e3304”)},{
    $push:{
    “relationships”:{
    “fname”:”xiong”,”lname”:”lan”}}})

"_id" : ObjectId("4ffcb2ed65282ea95f7e3304"),

"age" : 23,

"favorite" : {
    

    "1" : "reading",

    "2" : "swimming",

    "3" : "listening music"

},

"fname" : "jeff",

"height" : 166,

"lname" : "jiang",

"relationships" : [

    {
    

        "fname" : "deng",

        "lname" : "pan"

    },

    {
    

        "fname" : "qiang",

        "lname" : "he"

    },

    {
    

        "fname" : "dongren",

        "lname" : "zeng"

    },

    {
    

        "fname" : "xiong",

        "lname" : "lan"

    }

]

2. Delete an element at the end of the array

Do... On the array “ reduce ” operation , Can achieve pair array “ reduce ” There are two modifiers for the purpose ,pop and pull

db.user.update({
    “_id” : ObjectId(“4ffcb2ed65282ea95f7e3304”)},{
    $pop:{
    “relationships”:1}})

"_id" : ObjectId("4ffcb2ed65282ea95f7e3304"),

"age" : 23,

"favorite" : {
    

    "1" : "reading",

    "2" : "swimming",

    "3" : "listening music"

},

"fname" : "jeff",

"height" : 166,

"lname" : "jiang",

"relationships" : [

    {
    

        "fname" : "deng",

        "lname" : "pan"

    },

    {
    

        "fname" : "qiang",

        "lname" : "he"

    },

    {
    

        "fname" : "dongren",

        "lname" : "zeng"

    },

]

3. Delete an element at the beginning of the array

What should I do to delete from the beginning of the array . It's simple , Put the above “1” Change to “-1”, It will reverse the operation

db.user.update({
    “_id” : ObjectId(“4ffcb2ed65282ea95f7e3304”)},{
    $pop:{
    “relationships”:-1}})

"_id" : ObjectId("4ffcb2ed65282ea95f7e3304"),

"age" : 23,

"favorite" : {
    

    "1" : "reading",

    "2" : "swimming",

    "3" : "listening music"

},

"fname" : "jeff",

"height" : 166,

"lname" : "jiang",

"relationships" : [


    {
    

        "fname" : "qiang",

        "lname" : "he"

    },

    {
    

        "fname" : "dongren",

        "lname" : "zeng"

    }

]

4. Delete an element from the middle of the array

Want to delete the middle of the array . At this time ,$pull Come in handy
pull You can delete the data in the middle of the array . Here's one more thing to note ,pull All matched data will be deleted

db.user.update({
    “_id” : ObjectId(“4ffcb2ed65282ea95f7e3304”)},{
    $pull:{
    “relationships”:{
    “fname”:”dongren”,”lname”:”zeng”}}})

"_id" : ObjectId("4ffcb2ed65282ea95f7e3304"),

"age" : 23,

"favorite" : {
    

    "1" : "reading",

    "2" : "swimming",

    "3" : "listening music"

},

"fname" : "jeff",

"height" : 166,

"lname" : "jiang",

"relationships" : [

    {
    

        "fname" : "qiang",

        "lname" : "he"

    },

    {
    

        "fname" : "xiong",

        "lname" : "lan"

    }

]

5. Filter element

1. We insert the same data into the array , It can be inserted into the array normally . And in the actual production environment , We don't want to see such a result ,
that , Here are two more modifiers that you can use ：ne and addToSet.$ne Mainly used to judge , If there is this value in array , Do not insert ; No, just insert it

db.user.update({
    “relationships.fname”:{
    ne:"xiong"}},{
    set:{
    “fname”:”xiong”,”lname”:”lan”}})

"_id" : ObjectId("4ffcb2ed65282ea95f7e3304"),

"age" : 23,

"favorite" : {
    

    "1" : "reading",

    "2" : "swimming",

    "3" : "listening music"

},

"fname" : "jeff",

"height" : 166,

"lname" : "jiang",

"relationships" : [

    {
    

        "fname" : "qiang",

        "lname" : "he"

    },

    {
    

        "fname" : "xiong",

        "lname" : "lan"

    },


]

2.ddToSet Than ne Better to use , It can determine whether the data exists by itself , And it and each Use a combination of , You can also insert multiple data into an array at the same time , This is a ne It can't be done

db.user.update({
    “_id” : ObjectId(“4ffcb2ed65282ea95f7e3304”)},{
    addToSet:{
    "relationships":{
    each:[{
    “fname”:”xiong”,”lname”:”lan”},
{
    “fname”:”dongren”,”lname”:”zeng”}]}}})

"_id" : ObjectId("4ffcb2ed65282ea95f7e3304"),

"age" : 23,

"favorite" : {
    

    "1" : "reading",

    "2" : "swimming",

    "3" : "listening music"

},

"fname" : "jeff",

"height" : 166,

"lname" : "jiang",

"relationships" : [

    {
    

        "fname" : "qiang",

        "lname" : "he"

    },

    {
    

        "fname" : "xiong",

        "lname" : "lan"

    },

    {
    

        "fname" : "xiong",

        "lname" : "lan"

    },

    {
    

        "fname" : "dongren",

        "lname" : "zeng"

    }

]

In a modification statement , We want to insert... At the same time {“fname”:”xiong”,”lname”:”lan”},

{“fname”:”dongren”,”lname”:”zeng”} Two figures , But in the original array ,
{“fname”:”xiong”,”lname”:”lan”} This data already exists , So it just inserted the back one . We have achieved what we want . therefore , I personally prefer to use $addToSet

6. Operate on some of them

Sometimes an array has multiple values , And we just want to operate on some of them . If we copy down the whole document , That's too much trouble and stupid . Fortunately mongodb It provides us with two simple methods ： By position or operator “$”. Let's take a look at how these two methods are used . The first is to operate through the array position . Arrays are all based on 0 At the beginning , You can use subscripts directly as keys to select elements . for example , We want to add the age key value pair to the first data of the array , We can do this ：

 db.user.update({
    “_id” : ObjectId(“4ffcb2ed65282ea95f7e3304”)},{
    $set:{
    “relationships.0.age”:22}})

"_id" : ObjectId("4ffcb2ed65282ea95f7e3304"),

"age" : 23,

"favorite" : {
    

    "1" : "reading",

    "2" : "swimming",

    "3" : "listening music"

},

"fname" : "jeff",

"height" : 166,

"lname" : "jiang",

"relationships" : [

    {
    

        "age" : 22,

        "fname" : "qiang",

        "lname" : "he"

    },

    {
    

        "fname" : "deng",

        "lname" : "pan"

    },

    {
    

        "fname" : "xiong",

        "lname" : "lan"

    }

]

But in many cases , Without querying the document in advance, we don't know to modify the subscript of the elements of the array . Then the positioning operator “$” It's easy to use . It is used to locate the matching elements of the query document , And update . Let's see how it works ：

db.user.update({
    “relationships.fname”:”xiong”},{
    set:{
    "relationships..age”:22}})

"_id" : ObjectId("4ffcb2ed65282ea95f7e3304"),

"age" : 23,

"favorite" : {
    

    "1" : "reading",

    "2" : "swimming",

    "3" : "listening music"

},

"fname" : "jeff",

"height" : 166,

"lname" : "jiang",

"relationships" : [

    {
    

        "age" : 22,

        "fname" : "qiang",

        "lname" : "he"

    },

    {
    

        "age" : 22,

        "fname" : "deng",

        "lname" : "pan"

    },

    {
    

        "age" : 22,

        "fname" : "xiong",

        "lname" : "lan"

    }

]

7 mongodb in $ The role of

Definition

Locator $ To determine the position of an element to be updated in the array , Instead of specifying the position of the element in the array .
usage

1. Update the values in the array
1） Grammar format

{
    "<array>.$": value}

2） Example
Create set students There are the following documents ：

db.students.insert([
   {
     "_id" : 1, "grades" : [ 85, 80, 80 ] },
   {
     "_id" : 2, "grades" : [ 88, 90, 92 ] },
   {
     "_id" : 3, "grades" : [ 85, 100, 90 ] }
])

take grades The first value in the array is 80 Updated to 82, If you don't know the exact location of the first value , You can write like this ：

db.students.updateOne(
   {
     _id: 1, grades: 80 },
   {
     $set: {
     "grades.$" : 82 } }
)

Locator $ Like a placeholder , Match the first value that matches the query criteria .
2. Update the document in the array
Locators make it easy to update arrays that contain embedded documents . To get the field attribute value embedded in the document , Use the dot symbol after . Such as the following syntax format description

1） Grammar format

db.collection.update(
   {
     <query selector> },
   {
     <update operator>: {
     "array.$.field" : value } }
)

2） give an example
hypothesis students Collection grades The array contains the following embedded documents ：

{
    
  _id: 4,
  grades: [
     {
     grade: 80, mean: 75, std: 8 },
     {
     grade: 85, mean: 90, std: 5 },
     {
     grade: 85, mean: 85, std: 8 }
  ]
}

Use $ Locator to update grades Fields in the document in the array std Value , The updated document is the first match grade The value is 85 Documents . as follows ：

db.students.updateOne(
   {
     _id: 4, "grades.grade": 85 },
   {
     $set: {
     "grades.$.std" : 6 } }
)

The updated result is ：

{
    
   "_id" : 4,
   "grades" : [
      {
     "grade" : 80, "mean" : 75, "std" : 8 },
      {
     "grade" : 85, "mean" : 90, "std" : 6 },
      {
     "grade" : 85, "mean" : 85, "std" : 8 }
   ]
}