$setEquals (aggregation)

Definition定义

$setEquals

Compares two or more arrays and returns true if they have the same distinct elements and false otherwise.比较两个或多个数组，如果它们具有相同的不同元素，则返回true，否则返回false。

$setEquals has the following syntax:语法如下：

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

The arguments can be any valid expression as long as they each resolve to an array. 参数可以是任何有效的表达式，只要它们各自解析为一个数组。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

$setEquals performs set operation on arrays, treating arrays as sets. 对数组执行集合操作，将数组视为集合。If an array contains duplicate entries, $setEquals ignores the duplicate entries. 如果数组包含重复项，$setEquals将忽略重复项。$setEquals ignores the order of the elements.忽略元素的顺序。

If a set contains a nested array element, $setEquals does not descend into the nested array but evaluates the array at top-level.如果集合包含嵌套数组元素，则$setEquals不会下降到嵌套数组中，而是在顶层计算数组。

Example示例

Consider an experiments collection with the following documents:考虑一个包含以下文档的experiments集合：

{ "_id" : 1, "A" : [ "red", "blue" ], "B" : [ "red", "blue" ] }
{ "_id" : 2, "A" : [ "red", "blue" ], "B" : [ "blue", "red", "blue" ] }
{ "_id" : 3, "A" : [ "red", "blue" ], "B" : [ "red", "blue", "green" ] }
{ "_id" : 4, "A" : [ "red", "blue" ], "B" : [ "green", "red" ] }
{ "_id" : 5, "A" : [ "red", "blue" ], "B" : [ ] }
{ "_id" : 6, "A" : [ "red", "blue" ], "B" : [ [ "red" ], [ "blue" ] ] }
{ "_id" : 7, "A" : [ "red", "blue" ], "B" : [ [ "red", "blue" ] ] }
{ "_id" : 8, "A" : [ ], "B" : [ ] }
{ "_id" : 9, "A" : [ ], "B" : [ "red" ] }

The following operation uses the $setEquals operator to determine if the A array and the B array contain the same elements:以下操作使用$setEquals运算符确定A数组和B数组是否包含相同的元素：

db.experiments.aggregate(
   [
     { $project: { A: 1, B: 1, sameElements: { $setEquals: [ "$A", "$B" ] }, _id: 0 } }
   ]
)

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

{ "A" : [ "red", "blue" ], "B" : [ "red", "blue" ], "sameElements" : true }
{ "A" : [ "red", "blue" ], "B" : [ "blue", "red", "blue" ], "sameElements" : true }
{ "A" : [ "red", "blue" ], "B" : [ "red", "blue", "green" ], "sameElements" : false }
{ "A" : [ "red", "blue" ], "B" : [ "green", "red" ], "sameElements" : false }
{ "A" : [ "red", "blue" ], "B" : [ ], "sameElements" : false }
{ "A" : [ "red", "blue" ], "B" : [ [ "red" ], [ "blue" ] ], "sameElements" : false }
{ "A" : [ "red", "blue" ], "B" : [ [ "red", "blue" ] ], "sameElements" : false }
{ "A" : [ ], "B" : [ ], "sameElements" : true }
{ "A" : [ ], "B" : [ "red" ], "sameElements" : false }