Mongodb tutorial Chapter 08 comparison operators

This article will introduce MongoDB Some comparison operators commonly used to find documents in , Include $eq、$gt、$gte、$lt、$lte、$ne、$in as well as $nin.

$eq Operator

$eq Operator is used to match fields equal to （=） The document with the specified value .$eq The syntax of the operator is as follows ：

{
     <field>: {
     $eq: <value> } }

The above grammar is equivalent to the following writing ：

{
    <field>: <value>}

Let's create a collection products As a demonstration in the following ：

db.products.insertMany([
    {
     "_id" : 1, "name" : "xPhone", "price" : 799, "releaseDate": ISODate("2011-05-14"), "spec" : {
     "ram" : 4, "screen" : 6.5, "cpu" : 2.66 },"color":["white","black"],"storage":[64,128,256]},
    {
     "_id" : 2, "name" : "xTablet", "price" : 899, "releaseDate": ISODate("2011-09-01") , "spec" : {
     "ram" : 16, "screen" : 9.5, "cpu" : 3.66 },"color":["white","black","purple"],"storage":[128,256,512]},
    {
     "_id" : 3, "name" : "SmartTablet", "price" : 899, "releaseDate": ISODate("2015-01-14"), "spec" : {
     "ram" : 12, "screen" : 9.7, "cpu" : 3.66 },"color":["blue"],"storage":[16,64,128]},
    {
     "_id" : 4, "name" : "SmartPad", "price" : 699, "releaseDate": ISODate("2020-05-14"),"spec" : {
     "ram" : 8, "screen" : 9.7, "cpu" : 1.66 },"color":["white","orange","gold","gray"],"storage":[128,256,1024]},
    {
     "_id" : 5, "name" : "SmartPhone", "price" : 599,"releaseDate": ISODate("2022-09-14"), "spec" : {
     "ram" : 4, "screen" : 9.7, "cpu" : 1.66 },"color":["white","orange","gold","gray"],"storage":[128,256]}
 ])

The following example uses $eq Operator to find products Collection price Field equals 899 All documents of ：

db.products.find({
    
    price: {
    
        $eq: 899
    }
}, {
    
    name: 1,
    price: 1
})

We can also use the following equivalent expression ：

db.products.find({
    
    price: 899
}, {
    
    name: 1,
    price: 1
})

The return results of the above two examples are the same ：

[
  {
     _id: 2, name: 'xTablet', price: 899 },
  {
     _id: 3, name: 'SmartTablet', price: 899 }
]

The following example uses $eq Operator to find nested documents spec Middle field ram The value is equal to the 4 Documents ：

db.products.find({
    
    "spec.ram": {
    
        $eq: 4
    }
}, {
    
    name: 1,
    "spec.ram": 1
})

The documents returned from the query are as follows ：

[
  {
     _id: 1, name: 'xPhone', spec: {
     ram: 4 } },
  {
     _id: 5, name: 'SmartPhone', spec: {
     ram: 4 } }
]

The following example uses $eq Operator to find products Array in the collection color contain “black” The document of the element ：

db.products.find({
    
    color: {
    
        $eq: "black"
    }
}, {
    
    name: 1,
    color: 1
})

The documents returned from the query are as follows ：

[
  {
     _id: 1, name: 'xPhone', color: [ 'white', 'black' ] },
  {
     _id: 2, name: 'xTablet', color: [ 'white', 'black', 'purple' ] }
]

$gt Operator

$gt Operator is used to match fields larger than （>） The document with the specified value .$gt The syntax of the operator is as follows ：

{
     field: {
     $gt: value}}

The following example uses $gt Operator to find a set products in price Greater than 699 Documents ：

db.products.find({
    
    price: {
    
        $gt: 699
    }
}, {
    
    name: 1,
    price: 1
})

The result of the query is as follows ：

[
  {
     _id: 1, name: 'xPhone', price: 799 },
  {
     _id: 2, name: 'xTablet', price: 899 },
  {
     _id: 3, name: 'SmartTablet', price: 899 }
]

$gte Operator

$gte Operator is used to match fields greater than or equal to （>=） The document with the specified value .$gte The syntax of the operator is as follows ：

{
    field: {
    $gte: value} }

The following example uses $gte Operator to find a set products Embed documents in spec Field of screen Greater than or equal to 9.5 Documents ：

db.products.find({
    
    "spec.screen": {
    
        $gte: 9.5
    }
}, {
    
    name: 1,
    "spec.screen": 1
})

The results are as follows ：

[
  {
     _id: 2, name: 'xTablet', spec: {
     screen: 9.5 } },
  {
     _id: 3, name: 'SmartTablet', spec: {
     screen: 9.7 } },
  {
     _id: 4, name: 'SmartPad', spec: {
     screen: 9.7 } },
  {
     _id: 5, name: 'SmartPhone', spec: {
     screen: 9.7 } }
]

$lt Operator

$lt Operator is used to match fields less than （<） The document with the specified value .$lt The syntax of the operator is as follows ：

{
    field: {
    $lt: value} }

The following example uses $lt Operator to find a set products Array fields in storage At least one less than 128 The document of the element ：

db.products.find({
    
    storage: {
    
        $lt: 128
    }
}, {
    
    name: 1,
    storage: 1
})

The documents returned from the query are as follows ：

[
  {
     _id: 1, name: 'xPhone', storage: [ 64, 128, 256 ] },
  {
     _id: 3, name: 'SmartTablet', storage: [ 16, 64, 128 ] }
]

$lte Operator

$lte Operator is used to match fields less than or equal to （<=） The document with the specified value .$lte The syntax of the operator is as follows ：

{
    field: {
    $lte: value} }

The following example uses $lte Operator to find a set products The release date of is earlier than or equal to 2015-01-11 All documents of ：

db.products.find({
    
    "releaseDate": {
    
        $lte: new ISODate('2015-01-01')
    }
}, {
    
    name: 1,
    releaseDate: 1
});

The documents returned from the query are as follows ：

[
  {
    
    _id: 1,
    name: 'xPhone',
    releaseDate: ISODate("2011-05-14T00:00:00.000Z")
  },
  {
    
    _id: 2,
    name: 'xTablet',
    releaseDate: ISODate("2011-09-01T00:00:00.000Z")
  }
]

$ne Operator

$ne Operator matching field is not equal to （<>） The document with the specified value .$ne The syntax of the operator is as follows ：

{
     field: {
    $ne: value}}

The following example uses $ne Operator to find a set products in price It's not equal to 899 Documents ：

db.products.find({
    
    price: {
    
        $ne: 899
    }
}, {
    
    name: 1,
    price: 1
})

The documents returned from the query are as follows ：

[
  {
     _id: 1, name: 'xPhone', price: 799 },
  {
     _id: 4, name: 'SmartPad', price: 699 },
  {
     _id: 5, name: 'SmartPhone', price: 599 },
  {
     _id: 6, name: 'xWidget' }
]

$in Operator

$in Operator matching field equals （=） Documents with arbitrary values in the array .$in The syntax of the operator is as follows ：

{
     field: {
     $in: [<value1>, <value2>,...] }}

If field Only one value ,$in Operator matches a document whose field is equal to any value in the array . If field It's also an array ,$in Operator matches that the array contains an array [value1, value2,…] Document with any value in .

Array list value1, value2, … It can be a list of constants or a list of regular expressions .

A regular expression is a set of characters that define a search pattern , For example, regular expressions /\d+/ Match any array , Include 1,123,1234 etc. .

The following example uses $in Operator to find products Collection price Field equals 599 perhaps 799 Documents ：

db.products.find({
    
    price: {
    
        $in: [699, 799]
    }
}, {
    
    name: 1,
    price: 1
})

The documents returned from the query are as follows ：

[
  {
     _id: 1, name: 'xPhone', price: 799 },
  {
     _id: 4, name: 'SmartPad', price: 699 }
]

$nin Operator

$nin Operator matching field is not equal to （!=） Documents with arbitrary values in the array , Or specify a document where the field does not exist .$nin The syntax of the operator is as follows ：

{
     field: {
     $nin: [ <value1>, <value2> ...]} }

The following example uses $nin Operator to find products Collection price Field is neither equal to 599 Also is not equal to 799 Documents ：

db.products.find({
    
    price: {
    
        $nin: [699, 799]
    }
}, {
    
    name: 1,
    price: 1
})

The documents returned from the query are as follows ：

[
  {
     _id: 2, name: 'xTablet', price: 899 },
  {
     _id: 3, name: 'SmartTablet', price: 899 },
  {
     _id: 5, name: 'SmartPhone', price: 599 }
]

The following example uses $nin Operator to find color The array field does not contain any matching regular expressions /^g+/ perhaps /^w+/ The document of the element ：

db.products.find({
    
    color: {
    
        $nin: [/^g+/, /^w+/]
    }
}, {
    
    name: 1,
    color: 1
})

The documents returned from the query are as follows ：

[ {
     _id: 3, name: 'SmartTablet', color: [ 'blue' ] } ]