mongodb:3.6

數(shù)據(jù)

1，user表

{
    "_id" : ObjectId("5b69062240a6d80a6cece003"),
    "name" : "小明",
    "age" : 28,
    "createtime" : ISODate("2018-08-07T02:38:26.601Z"),
    "_class" : "com.xiangpeng.bo.UserBo"
}

2膀懈，orders表

/* 1 */
{
    "_id" : ObjectId("5b69062240a6d80a6cece004"),
    "uid" : ObjectId("5b69062240a6d80a6cece003"),
    "money" : 10.0,
    "createtime" : ISODate("2018-08-07T02:38:26.601Z"),
    "produce" : "產(chǎn)品1",
    "_class" : "com.xiangpeng.bo.OrderBo"
}

/* 2 */
{
    "_id" : ObjectId("5b6a5711c2eee4295c63768e"),
    "uid" : ObjectId("5b69062240a6d80a6cece003"),
    "money" : 20.0,
    "produce" : "產(chǎn)品2",
    "createtime" : ISODate("2018-08-07T02:38:26.601Z"),
    "_class" : "com.xiangpeng.bo.OrderBo"
}

查詢

1,mongodb的多表查詢比較簡單,使用$lookup關(guān)鍵字即可:

db.user.aggregate([{$lookup:{from:"orders",localField:"_id",foreignField:"uid",as:"orders"}}])

結(jié)果:

{
    "_id" : ObjectId("5b69062240a6d80a6cece003"),
    "name" : "小明",
    "age" : 28,
    "createtime" : ISODate("2018-08-07T02:38:26.601Z"),
    "_class" : "com.xiangpeng.bo.UserBo",
    "orders" : [ 
        {
            "_id" : ObjectId("5b69062240a6d80a6cece004"),
            "uid" : ObjectId("5b69062240a6d80a6cece003"),
            "money" : 10.0,
            "createtime" : ISODate("2018-08-07T02:38:26.601Z"),
            "produce" : "產(chǎn)品1",
            "_class" : "com.xiangpeng.bo.OrderBo"
        }, 
        {
            "_id" : ObjectId("5b6a5711c2eee4295c63768e"),
            "uid" : ObjectId("5b69062240a6d80a6cece003"),
            "money" : 20.0,
            "produce" : "產(chǎn)品2",
            "createtime" : ISODate("2018-08-07T02:38:26.601Z"),
            "_class" : "com.xiangpeng.bo.OrderBo"
        }
    ]
}

參數(shù)解釋:
form:需要關(guān)聯(lián)的外表名,lookup進行查詢后會將所有符合條件的文檔封裝為一個list,as參數(shù)定義這個list的名字;

數(shù)據(jù)處理

使用$unwind將數(shù)據(jù)打散:

db.user.aggregate([
        {$lookup:{from:"orders",localField:"_id",foreignField:"uid",as:"orders"},
        {$unwind:"$orders"}
])

$unwind的作用是將文檔中的數(shù)組拆分為多條,拆分結(jié)果為:

/* 1 */
{
    "_id" : ObjectId("5b69062240a6d80a6cece003"),
    "name" : "小明",
    "age" : 28,
    "createtime" : ISODate("2018-08-07T02:38:26.601Z"),
    "_class" : "com.xiangpeng.bo.UserBo",
    "orders" : {
        "_id" : ObjectId("5b69062240a6d80a6cece004"),
        "uid" : ObjectId("5b69062240a6d80a6cece003"),
        "money" : 10.0,
        "createtime" : ISODate("2018-08-07T02:38:26.601Z"),
        "produce" : "產(chǎn)品1",
        "_class" : "com.xiangpeng.bo.OrderBo"
    }
}

/* 2 */
{
    "_id" : ObjectId("5b69062240a6d80a6cece003"),
    "name" : "小明",
    "age" : 28,
    "createtime" : ISODate("2018-08-07T02:38:26.601Z"),
    "_class" : "com.xiangpeng.bo.UserBo",
    "orders" : {
        "_id" : ObjectId("5b6a5711c2eee4295c63768e"),
        "uid" : ObjectId("5b69062240a6d80a6cece003"),
        "money" : 20.0,
        "produce" : "產(chǎn)品2",
        "createtime" : ISODate("2018-08-07T02:38:26.601Z"),
        "_class" : "com.xiangpeng.bo.OrderBo"
    }
}

數(shù)據(jù)過濾

現(xiàn)在可以對數(shù)據(jù)進行過濾,數(shù)據(jù)過濾的步驟應(yīng)該盡可能提前,但如果過濾條件中也需要篩選外表條件的話就沒辦法放前面了,過濾在聚合中使用$match

db.user.aggregate([
    {$lookup:{from:"orders",localField:"_id",foreignField:"uid",as:"orders"}},
    {$unwind:"$orders"},
    {$match:{name:"小明","orders.produce":"產(chǎn)品2"}}
])

查出小明買的產(chǎn)品2訂單
結(jié)果展示

/* 1 */
{
    "_id" : ObjectId("5b69062240a6d80a6cece003"),
    "name" : "小明",
    "age" : 28,
    "createtime" : ISODate("2018-08-07T02:38:26.601Z"),
    "_class" : "com.xiangpeng.bo.UserBo",
    "orders" : {
        "_id" : ObjectId("5b6a5711c2eee4295c63768e"),
        "uid" : ObjectId("5b69062240a6d80a6cece003"),
        "money" : 20.0,
        "produce" : "產(chǎn)品2",
        "createtime" : ISODate("2018-08-07T02:38:26.601Z"),
        "_class" : "com.xiangpeng.bo.OrderBo"
    }
}

如果對字段結(jié)果有要求可以使用$project進行字段篩選:

db.user.aggregate([
    {$lookup:{from:"orders",localField:"_id",foreignField:"uid",as:"orders"}},
    {$unwind:"$orders"},
    {$match:{name:"小明","orders.produce":"產(chǎn)品2"}},
    {$project:{name:"$name",age:"$age",produce:"$orders.produce",money:"$orders.money"}}])

再聚合中$可以用作引用相應(yīng)字段的值
結(jié)果為:

/* 1 */
{
    "_id" : ObjectId("5b69062240a6d80a6cece003"),
    "name" : "小明",
    "age" : 28,
    "produce" : "產(chǎn)品2",
    "money" : 20.0
}