MongoDB聚合运算符：$setUnion

$setUnion聚合运算符返回两个或多个数组的并集。

语法

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

<expression>为可解析为数组的表达式。

使用

$setUnion对数组执行集合操作，将数组视为集合。如果数组包含重复元素，$setUnion会忽略重复元素，并且$setUnion也会忽略元素的顺序。

如果集合包含嵌套数组元素，$setUnion 不会进入嵌套数组，而对顶层对数组进行评估。

举例	结果
{ $setUnion: [ [ "a", "b", "a" ], [ "b", "a" ] ] }	[ "b", "a" ]
{ $setUnion: [ [ "a", "b" ], [ [ "a", "b" ] ] ] }	[ [ "a", "b" ], "b", "a" ]

举例

使用下面的脚本创建flowers集合：

db.flowers.insertMany( [{ "_id" : 1, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "rose", "orchid" ] },{ "_id" : 2, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "orchid", "rose", "orchid" ] },{ "_id" : 3, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "rose", "orchid", "jasmine" ] },{ "_id" : 4, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "jasmine", "rose" ] },{ "_id" : 5, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ ] },{ "_id" : 6, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ [ "rose" ], [ "orchid" ] ] },{ "_id" : 7, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ [ "rose", "orchid" ] ] },{ "_id" : 8, "flowerFieldA" : [ ], "flowerFieldB" : [ ] },{ "_id" : 9, "flowerFieldA" : [ ], "flowerFieldB" : [ "rose" ] }
] )

下面的操作使用$setUnion运算符返回在数组flowerFieldA或数组flowerFieldB中出现的元素的数组，就是两个数组的并集：

db.flowers.aggregate([{ $project: { flowerFieldA:1, flowerFieldB: 1, allValues: { $setUnion: [ "$flowerFieldA", "$flowerFieldB" ] }, _id: 0 } }]
)

操作返回下面的结果：

{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ "rose", "orchid" ], "allValues": [ "orchid", "rose" ] }
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ "orchid", "rose", "orchid" ], "allValues": [ "orchid", "rose" ] }
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ "rose", "orchid", "jasmine" ], "allValues": [ "orchid", "rose", "jasmine" ] }
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ "jasmine", "rose" ], "allValues": [ "orchid", "rose", "jasmine" ] }
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ ], "allValues": [ "orchid", "rose" ] }
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ [ "rose" ], [ "orchid" ] ], "allValues": [ "orchid", "rose", [ "rose" ], [ "orchid" ] ] }
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ [ "rose", "orchid" ] ], "allValues": [ "orchid", "rose", [ "rose", "orchid" ] ] }
{ "flowerFieldA": [ ], "flowerFieldB": [ ], "allValues": [ ] }
{ "flowerFieldA": [ ], "flowerFieldB": [ "rose" ], "allValues": [ "rose" ] }