Question

我需要将3个集合与多个$lookup聚合在一起我在C＃驱动程序中尝试过，它允许我进行$lookup用户收集，但无法执行第二次$lookup进行设置收集。

有人可以帮忙吗？

db.Transactions.aggregate([
    {
        $lookup:
        {
            from: "Account",
            localField: "AccountId",
            foreignField: "_id",
            as: "Account"
        }
    },
       {
           $lookup:
        {
            from: "User",
            localField: "UserId",
            foreignField: "_id",
            as: "User"
        }
       }
    ])
    .match({
    })
    .project({})

这是C＃代码：

 var account = _dbClient.GetDatabase(_dbName).GetCollection<Account>("Accounts");
var user = _dbClient.GetDatabase(_dbName).GetCollection<User>("Users");
var transaction = _dbClient.GetDatabase(_dbName).GetCollection<Transaction>("Transactions");

var result = (from t in transaction.AsQueryable()
              join a in account.AsQueryable() on t.AccountId equals a.Id
              join u in user.AsQueryable() on t.UserId equals u.Id into userList
              from acc in userList.DefaultIfEmpty()
              where acc.CompanyName.ToLower().Contains(companyName) && c.CreatedDate >= fromDate && c.CreatedDate <= toDate
              select new TransactionHistory
              {
                   Id = t.Id,
                   CompanyName = acc.CompanyName,
                   UserId = u.UserId
                   FirstName = u.FirstName
              }).ToList();

我使用Linq收到错误$project or $group does not support {document}.。

Answer 1

我需要通过多个$ lookup将3个集合聚合在一起

给出以下类别：

public class Transactions
{
    public ObjectId Id { get; set; }
    public int UserId { get; set; }
    public int AccountId { get; set; }
    public int SettingId { get; set; }
}
public class Account
{
    public int Id {get; set;}
    public int Name {get; set;}
}
public class User
{
    public int Id {get; set;}
    public int Name {get; set;}
}
public class Setting
{
    public int Id {get; set;}
    public int Name {get; set;}
}

您可以使用$lookup（当前为v2.9）执行以下多个MongoDB .NET/C# driver阶段：

var collection = database.GetCollection（“ transactions”）;

var docs = collection.Aggregate()
                     .Lookup("account", "AccountId", "_id", "asAccounts")
                     .Lookup("user", "UserId", "_id", "asUsers")
                     .Lookup("setting", "SettingId", "_id", "asSettings")
                     .As<BsonDocument>()
                     .ToList();

foreach (var doc in docs) {
    Console.WriteLine(doc.ToJson());
}

如果要过滤特定值，可以在之间/之前/之后添加Match。请记住，在每个Lookup阶段之后都对文档进行了修改。

值得一提的是，如果您需要在常见操作中加入多个集合，则应重新考虑database data model。有关更多信息，请参见Schema Design: Summary。

如何使用Mongodb C＃驱动程序加入多个集合

1 个答案: