我有一个简单的数据库,包含元素的子集:
{ "_id" : ObjectId("5019eb2356d80cd005000000"),
"photo" : "/pub/photos/file1.jpg",
"comments" : [
{
"name" : "mike",
"message" : "hello to all"
},
{
"name" : "pedro",
"message" : "hola a todos"
}
]
},
{ "_id" : ObjectId("5019eb4756d80cd005000001"),
"photo" : "/pub/photos/file2.jpg",
"comments" : [
{
"name" : "luca",
"message" : "ciao a tutti"
},
{
"name" : "stef",
"message" : "todos bien"
},
{
"name" : "joice",
"message" : "vamos a las playa"
}
]
}
当我执行子集查找时:db.products.find({},{"comments.name":1})
我收到这个结构:
[
{
"_id" : ObjectId("5019eb2356d80cd005000000"),
"comments" : [
{
"name" : "mike"
},
{
"name" : "pedro"
}
]
},
{
"_id" : ObjectId("5019eb4756d80cd005000001"),
"comments" : [
{
"name" : "luca"
},
{
"name" : "stef"
},
{
"name" : "joice"
}
]
}
]
但我想得到一个简单的一维数组,像这样(或类似):
[
{
"name" : "mike"
},
{
"name" : "pedro"
},
{
"name" : "luca"
},
{
"name" : "stef"
},
{
"name" : "joice"
}
]
我需要用mongophp官方驱动程序来实现这个查询,但语言并不重要,我只想了解通过mongoshell 可以通过什么逻辑来实现这一点
tnk!
最简单的选择是使用distinct():
>db.photos.distinct("comments.name");
[ "mike", "pedro", "joice", "luca", "stef" ]
下面是另一个使用JavaScript的例子:
// Array to save results
> var names = []
// Find comments and save names
> db.photos.find({},{"comments.name":1}).forEach(
function(doc) { doc.comments.forEach(
function(comment) {names.push(comment.name)})
})
// Check the results
> names
[ "mike", "pedro", "luca", "stef", "joice" ]
以下是即将发布的MongoDB 2.2:中使用新聚合框架的示例
db.photos.aggregate(
{ $unwind : "$comments" },
{ $group : {
_id: "names",
names: { $addToSet : "$comments.name" }
}},
{ $project : {
'_id' : 0,
'names' : 1,
}}
)