MongoDB $mod 运算符

MongoDB $mod 运算符 介绍

MongoDB 提供了多种算术表达式运算符。$mod 运算符就是这些运算符之一。$mod 运算符用于聚合管道阶段。$mod 运算符用于将一个数字除以另一个数字并返回余数。换句话说，第一个数字是被除数，第二个数字是除数。

MongoDB $mod 运算符 语法

{ $mod: [ < expression 1 >, < expression 2 > ] }  

这 可以是任何解析为数字的有效表达式。

MongoDB $mod 运算符 例子

在以下示例中，我们正在使用：

Database: Yiidian
Collection: items  
Document: Ten documents that contain the details of the items  

>db.items.find().pretty()
{
    {
        "_id" : 1,
        "item_name" : "Apple",
        "total_Price" : null,
        "quantity" : 40,
    }
    {
        "_id" : 2,
        "item_name" : "Banana",
        "total_Price" : 1000,
        "quantity" : 72,
    }
    {
        "_id" : 3,
        "item_name" : "Cherry",
        "total_Price" : 215,
        "quantity" : 25,
    }
    {
        "_id" : 4,
        "item_name" : "Apple",
        "total_Price" : null,
        "quantity" : 25,
    }
    {
        "_id" : 5,
        "item_name" : "Banana",
        "total_Price" : 400,
        "quantity" : 35,
    }
    {
        "_id" : 6,
        "item_name" : "Banana",
        "total_Price" : 510,
        "quantity" : 100,
    }
    {
        "_id" : 7,
        "item_name" : "Cherry",
        "total_Price" : 500,
        "quantity" : 41,
    }
    {
        "_id" : 8,
        "item_name" : "Rasbhari",
        "total_Price" : 80,
        "quantity" : "Ten",
    }
    {
        "_id" : 9,
        "item_name" : "Banana",
        "total_Price" : 205,
        "quantity" : 10,
    }
    {
        "_id" : 10,
        "item_name" : "Apple",
        "total_Price" : 95,
        "quantity" : null,
    }
}

示例 1：使用 $mod 运算符查找提醒

在此示例中，我们将使用 $mod 运算符将“total_Price”字段的值除以“quantity”字段的值来找到余数。

db.item.aggregate(  
 [  
   {$match: {item_name : "Banana"}},  
      {  
          $project:   
              {  
                item_name : 1,  
                total_Price : 1,  
                quantity : 1,  
                remainderValue : {$mod: ["$total_Price", "$quantity"]}  
               }  
      }  
 ]  
)  

输出结果为：

{
    "_id" : 2,
    "item_name" : "Banana",
    "total_Price" : 1000,
    "quantity" : 72,
    "remainderValue" : 64
}
{
    "_id" : 5,
    "item_name" : "Banana",
    "total_Price" : 400,
    "quantity" : 35,
    "remainderValue" : 15
}
{
    "_id" : 6,
    "item_name" : "Banana",
    "total_Price" : 510,
    "quantity" : 100,
    "remainderValue" : 10
}
{
    "_id" : 9,
    "item_name" : "Banana",
    "total_Price" : 205,
    "quantity" : 10,
    "remainderValue" : 5
}  

示例 2：错误的数据类型

$mod 运算符仅支持数字数据类型。如果值是字符串，则 $mod 运算符返回错误。

{ "_id" : 8, "item_name" : "Rasbhari", "total_Price" : 80, "quantity" : "Ten", }  

db.item.aggregate(  
 [  
   {$match: {item_name : "Rasbhari"}},  
      {  
          $project:   
              {  
                item_name : 1,  
                total_Price : 1,  
                quantity : 1,  
                remainderValue : {$mod: ["$total_Price", "$quantity"]}  
               }  
      }  
 ]  
)  

输出结果为：

uncaught exception: Error: command failed: {
	"ok" : 0,
	"errmsg" : "$mod only supports numeric types, not string and double",
	"code" : 16611,
	"codeName" : "Location16611"
} : aggregate failed :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
doassert@src/mongo/shell/assert.js:18:14
_assertCommandWorked@src/mongo/shell/assert.js:639:17
assert.commandWorked@src/mongo/shell/assert.js:729:16
DB.prototype._runAggregate@src/mongo/shell/db.js:266:5
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1058:12
@(shell):1:1 

示例 3：Null值

在这个例子中，我们将通过使用 $mod 运算符将“total_Price”字段的值除以苹果中的“quantity”字段来找到余数。

db.item.aggregate(  
 [  
   {$match: {item_name : "Apple"}},  
      {  
          $project:   
              {  
                item_name : 1,  
                total_Price : 1,  
                quantity : 1,  
                remainderValue : {$mod: ["$total_Price", "$quantity"]}  
               }  
      }  
 ]  
)  

输出结果为：

{
    "_id" : 1,
    "item_name" : "Apple",
    "total_Price" : null,
    "quantity" : 40,
    "remainderValue" : null
}
{
    "_id" : 4,
    "item_name" : "Apple",
    "total_Price" : null,
    "quantity" : 25,
    "remainderValue" : null    
}
{
    "_id" : 10,
    "item_name" : "Apple",
    "total_Price" : 95,
    "quantity" : null,
    "remainderValue" : null
}