Mongodb C# - 仅当嵌套数组的嵌套元素符合条件时才进行聚合 $push

Question

我已经在网上看了很多，但我找不到解决办法...

有一个例子是我的类和对象：

类:

public class A {
    [BsonId]
    public int _id {get; set;}
    public List<B> ListOfB {get; set;}
    public TypeA Type {get; set;}
}

public class B {
    public int _id {get; set;}
    public int PersonId {get; set;}
    public Person Person {get; set;} // This one is not save on the DB, it is retrieved through a Lookup
    public int Type {get; set;}
}

public class Person {
    [BsonId]
    public int _id {get; set;}
    public string Name {get; set;}
}

对象：

{
    "_id": 0;
    "Type", 0,
    "ListOfB": [
        {
            "_id": 0,
            "PersonId": 300,
            "Type": 0
        },
        {
            "_id": 1,
            "PersonId": 24,
            "Type": 0
        },
        {
            "_id": 2,
            "PersonId": 59,
            "Type": 1
        }
    ]
},
{
    "_id": 1;
    "Type", 1,
    "ListOfB": [
        {
            "_id": 0,
            "PersonId": 45,
            "Type": 1
        },
        {
            "_id": 1,
            "PersonId": 102,
            "Type": 0
        },
        {
            "_id": 2,
            "PersonId": 33,
            "Type": 1
        }
    ]
}
,
{
    "_id": 2;
    "Type", 1,
    "ListOfB": [
        {
            "_id": 0,
            "PersonId": 66,
            "Type": 1
        },
        {
            "_id": 1,
            "PersonId": 89,
            "Type": 0
        },
        {
            "_id": 2,
            "PersonId": 404,
            "Type": 0
        }
    ]
}

B是A集合的一部分，没有B集合。到目前为止，我已经做了类似这样的事情来检索对象：

BsonDocument groupMappingA = new BsonDocument();
groupMappingA.Add(new BsonElement("_id", "$_id"));

BsonDocument groupMappingB = new BsonDocument();
groupMappingB.Add(new BsonElement("_id", "$ListOfB._id"));
groupMappingB.Add(new BsonElement("PersonId", "$ListOfB.PersonId"));
groupMappingB.Add(new BsonElement("Person", "$ListOfB.Person"));
groupMappingB.Add(new BsonElement("Type", "$ListOfB.Type"));

groupMappingA.Add(new BsonElement("ListOfB", new BsonDocument(
                                                "$push", new BsonDocument(
                                                        "$cond", new BsonArray {
                                                            new BsonDocument("$eq", new BsonDocument("$ListOfB.Type", "0")),
                                                            new BsonDocument("$ListOfB", groupMappingB)
                                                        }
                                                )
                                            )
                                )
                );

AggregateUnwindOptions<A> unwindOptions = new AggregateUnwindOptions<A>() { PreserveNullAndEmptyArrays = true };
db.GetCollection<A>("A").Aggregate()
                        .match(x => x.Type == 1)
                        .Unwind("ListOfB", unwindOptions)
                        .Lookup("Person", "ListOfB.PersonId", "_id", "ListOfB.Person") // Here we set up Person through the ID saved in the object B
                        .Unwind("ListOfB.Person", unwindOptions)
                        .Group(groupMappingA)
                        .As<A>()
                        .ToList();

所以我想要实现的是检索所有对象 A，并过滤所有对象 B 以仅获取类型等于 0 的对象，对于每个对象 B，我应该具有人物，例如：

{
    "_id": 1;
    "Type", 1,
    "ListOfB": [
        {
            "_id": 1,
            "PersonId": 102,
            "Type": 0,
            "Person": { "_id": 102, "Name": "Billy" } 
        }
    ]
},
{
    "_id": 2;
    "Type", 1,
    "ListOfB": [
        {
            "_id": 1,
            "PersonId": 89,
            "Type": 0,
            "Person": { "_id": 89, "Name": "Finn" }
        },
        {
            "_id": 2,
            "PersonId": 404,
            "Type": 0,
            "Person": { "_id": 404, "Name": "Jake" }
        }
    ]
}

但这不起作用...我可以检索每个类型 1 的 A 对象，以及它们的 B 对象中的所有 Person 对象，但我得到了 B 的完整列表，而不仅仅是类型 0 的对象.

我先尝试在 Mongodb Compass 上做，但到目前为止，我没有成功，然后我在网上找了找，但找不到我要找的东西...我开始怀疑是否有可能在其嵌套列表中获取带有过滤器的对象？

预先感谢您的帮助。

Answer 1

我知道怎么做了，我把答案贴在这里以备不时之需。

BsonDocument groupMapping = new BsonDocument();
groupMapping.Add(new BsonElement("_id", new BsonDocument("$first", "$_id")));
groupMapping.Add(new BsonElement("ListOfB", new BsonDocument("$push", "$ListOfB")));

AggregateUnwindOptions<A> unwindOptions = new AggregateUnwindOptions<A>() { PreserveNullAndEmptyArrays = true };
db.GetCollection<A>("A").Aggregate()
                        .match(x => x.Type == 1)
                        .Unwind("ListOfB", unwindOptions)
                        .Match(new BsonDocument("ListOfB.Type", 0)) // Just put a match right after the Unwind, you'll be able to filter the elements of the list as you want.
                        .Lookup("Person", "ListOfB.PersonId", "_id", "ListOfB.Person")
                        .Unwind("ListOfB.Person", unwindOptions)
                        .Group(groupMapping)
                        .As<A>()
                        .ToList();

Mongodb C# - 仅当嵌套数组的嵌套元素符合条件时才进行聚合 $push

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