MongoDB - 基于另一个字段值的 $match

Question

我想从 SQL 中获得类似简单内部联接的结果，以获得相同 id_customer 的所有帐户。我几乎这样做了，但是我得到了像左连接这样的东西，而且我现在不知道如何过滤查询结果。

询问：

db.customer.aggregate([
    {
        $match: {
            "LOAN.AMOUNT": { $gte: 41000 }
        }
    },

    {
        $lookup: {
            from: "department",
            localField: "ID",
            foreignField: "ACCOUNT.ID_CUSTOMER",
            as: "customer"
        }
    },
    { $match: { "myArray": { $ne: [] } } },
    {
        $unwind: {
            path: "$customer",
            preserveNullAndEmptyArrays: false
        }
    }
    ,
    {
        $unwind: "$customer.ACCOUNT"
    },
    {
            $match: {
                "customer.ACCOUNT.ID_CUSTOMER": "$ID" 
            }
    },

]) 

实际结果：

empty

预期结果：

{ 
    "_id" : ObjectId("5dfccc28d29876c2988c7c05"), 
    "ID" : 4.0, 
    "SECOND_NAME" : "abc", 
    "FIRST_NAME" : "abc", 
    "ID_DISCOUNT" : {
        "ID" : 3.0, 
        "TITLE" : "abc", 
        "AMOUNT" : 5.0
    }, 
    "LOAN" : {
        "ID" : 4.0, 
        "AMOUNT" : 42750.0
    }, 
    "customer" : {
        "_id" : ObjectId("5dfb7f8f5861584bbaedf718"), 
        "ID" : 1.0, 
        "TITLE" : "abc", 
        "ADDRESS" : "abc", 
        "CITY" : "abc", 
        "ACCOUNT" : {
            "ID" : 10.0, 
            "ID_CUSTOMER" : 4.0, 
            "DATE_OPEN" : "2019-09-24 21:03:44"
        }
    }
}
{ 
    "_id" : ObjectId("5dfccc28d29876c2988c7c05"), 
    "ID" : 4.0, 
    "SECOND_NAME" : "abc", 
    "FIRST_NAME" : "abc ", 
    "ID_DISCOUNT" : {
        "ID" : 3.0, 
        "TITLE" : "abc", 
        "AMOUNT" : 5.0
    }, 
    "LOAN" : {
        "ID" : 4.0, 
        "AMOUNT" : 42750.0
    }, 
    "customer" : {
        "_id" : ObjectId("5dfb7f8f5861584bbaedf718"), 
        "ID" : 1.0, 
        "TITLE" : "abc", 
        "ADDRESS" : "abc", 
        "CITY" : "abc", 
        "ACCOUNT" : {
            "ID" : 11.0, 
            "ID_CUSTOMER" : 4.0, 
            "DATE_OPEN" : "2019-08-23 21:03:44"
        }
    }
}

具有相同 id_customer 的所有帐户的列表，但

$match: {
                    "customer.ACCOUNT.ID_CUSTOMER": "$ID" 
                }

不做我想做的事。

Answer 1

我找到了解决方案：使用 $expr 运算符

db.customer.aggregate([
    {
        $match: {
            "LOAN.AMOUNT": { $gte: 41000 }
        }
    },

    {
        $lookup: {
            from: "department",
            localField: "ID",
            foreignField: "ACCOUNT.ID_CUSTOMER",
            as: "customer"
        }
    },
    { $match: { "myArray": { $ne: [] } } },
    {
        $unwind: {
            path: "$customer",
            preserveNullAndEmptyArrays: false
        }
    }
    ,
    {
        $unwind: "$customer.ACCOUNT"
    },
    { $match: { $expr: { $eq: ["$customer.ACCOUNT.ID_CUSTOMER", "$ID"] } } },

])