$and (aggregation)¶

Definition定义¶

$and¶

Evaluates one or more expressions and returns true if all of the expressions are true or if evoked with no argument expressions. 对一个或多个表达式求值，如果所有表达式都为true，或者如果在没有参数表达式的情况下调用，则返回true。Otherwise, $and returns false.否则，$and返回false。

$and has the following syntax:语法如下所示：

{ $and: [ <expression1>, <expression2>, ... ] }

For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。

Behavior行为¶

$and uses short-circuit logic: the operation stops evaluation after encountering the first false expression.$and使用短路逻辑：操作在遇到第一个false表达式后停止计算。

In addition to the false boolean value, $and evaluates as false the following: null, 0, and undefined values. 除了false布尔值，$and还将以下值计算为false：null、0和undefined值。The $and evaluates all other values as true, including non-zero numeric values and arrays.$and将所有其他值计算为true，包括非零数值和数组。

Example示例¶

Create an example inventory collection with the following documents:使用以下文档创建一个示例inventory集合：

db.inventory.insertMany([
   { "_id" : 1, "item" : "abc1", description: "product 1", qty: 300 },
   { "_id" : 2, "item" : "abc2", description: "product 2", qty: 200 },
   { "_id" : 3, "item" : "xyz1", description: "product 3", qty: 250 },
   { "_id" : 4, "item" : "VWZ1", description: "product 4", qty: 300 },
   { "_id" : 5, "item" : "VWZ2", description: "product 5", qty: 180 }
])

The following operation uses the $and operator to determine if qty is greater than 100 and less than 250:以下操作使用$and运算符确定qty是否大于100且小于250：

db.inventory.aggregate(
   [
     {
       $project:
          {
            item: 1,
            qty: 1,
            result: { $and: [ { $gt: [ "$qty", 100 ] }, { $lt: [ "$qty", 250 ] } ] }
          }
     }
   ]
)

The operation returns the following results:操作返回以下结果：

{ "_id" : 1, "item" : "abc1", "qty" : 300, "result" : false }
{ "_id" : 2, "item" : "abc2", "qty" : 200, "result" : true }
{ "_id" : 3, "item" : "xyz1", "qty" : 250, "result" : false }
{ "_id" : 4, "item" : "VWZ1", "qty" : 300, "result" : false }
{ "_id" : 5, "item" : "VWZ2", "qty" : 180, "result" : true }