SQL 查询 LINQ INNER JOIN

Question

我需要将 SQL 查询转换为 LINQ，但不知道如何做。我有两个表：Bins 和 DataFromBins。 DataFromBins 包含引用 Bins.Id 的 BinId 列我的查询所做的是从 DataFromBins 中为每个 BinId 选择最新的行，并从 Bins 中为这些 BinId 加入一些数据。

请帮忙:(

SELECT BinId, Address, Lon, Lat, MaxFillLevel, Distance
FROM (
    SELECT DataFromBins.*
    FROM (
        SELECT DataFromBins.BinId, MAX(DataFromBins.Date) AS Date
        FROM DataFromBins
        GROUP BY DataFromBins.BinId
    ) AS latest_records
        INNER JOIN DataFromBins ON DataFromBins.BinId = latest_records.BinId
            AND DataFromBins.Date = latest_records.Date
) AS most_recent
    INNER JOIN Bins ON most_recent.BinId = Bins.Id

Answer 1

我猜你正在寻找下面的代码。诀窍是拆分子查询；）

假设 _db 是你的上下文。

var latestRecords = from t in _db.DataFromBins
               group t by t.BinId into g
                    select new
                    {
                        BinId = g.Key,
                        Date = (from t2 in g select t2.Date).Max()
                    };

var mostRecents = from itm in latestRecords
            join bin in _db.DataFromBins on new {BinId = itm.BinId,  Date =itm.Date  } equals new {BinId = bin.BinId ,  Date =bin.Date}
            select bin;

var finalQuery = from recent in mostRecents
            join bin _db.Bins on recent.BinId  equals bin.Id
            select new {
            bin.BinId,bin.Address, bin.Lon, bin.Lat, bin.MaxFillLevel, bin.Distance
            }

SQL 查询 LINQ INNER JOIN

SQL query to LINQ INNER JOIN

sql

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entity-framework

sql-to-linq-conversion

.net-core