如何在Linq C＃中使用多个条件

Question

This is my Linq query.

    var tmp = (from oScreenDef in listScreenDefinition
                       join oSynSession in listSynSession on
                               new { c1 = oScreenDef["venueCd"], c2 = oScreenDef["screenBytNum"] }
                               equals new { c1 = oSynSession["cinemaId"], c2 = oSynSession["screenDetails"].AsBsonDocument["num"] }
                       join oSessionAreaCount in listSessionAreaCount on
                                new { c1 = oScreenDef["venueCd"] }
                                equals new { c1 = oSessionAreaCount["cinemaId"] }
                       join oPrices in listSynPrices on
                               new { c1 = oScreenDef["venueCd"], c2 = oSynSession["cinemaId"] }
                               equals new { c1 = oPrices["cinemaId"], c2 = oPrices["cinemaId"] }
                       select new { doc = oSynSession[0], oScreenDef }).ToList();

In That oPrices object has cinemaID which should equal to oScreenDef["venueId"] and oSynSession["cinemaId"] .

For that i'm including two times oPrices["cinemaId"] as C1 and C2 ..

how can i avoid that and how can i improve this query.

please suggest better way..

All listScreenDefinition , listSessionAreaCount , listSynPrices are List<BsonDocument> items getting it from mongodb queries..

Answer 1

You can use let (see MSDN ) and remove the new { c1 = ... } . But I don't see much more optimization:

var tmp = (from oScreenDef in listScreenDefinition
           let oScreenDefVenueCd = oScreenDef["venueCd"]  // let clause creates a "local variable" Inside a LINQ query
           join oSynSession in listSynSession on
               new { c1 = oScreenDefVenueCd, c2 = oScreenDef["screenBytNum"] }
               equals new { c1 = oSynSession["cinemaId"], c2 = oSynSession["screenDetails"].AsBsonDocument["num"] }
           join oSessionAreaCount in listSessionAreaCount on
               oScreenDefVenueCd
               equals oSessionAreaCount["cinemaId"]
           join oPrices in listSynPrices on
               new { c1 = oScreenDefVenueCd, c2 = oSynSession["cinemaId"] }
               equals new { c1 = oPrices["cinemaId"], c2 = oPrices["cinemaId"] }
           select new { doc = oSynSession[0], oScreenDef }).ToList();

Update

public class MyItem
{
    public SynSession Doc;
    public ScreenDef ScreenDef;

    public MyItem(SynSession doc, ScreenDef screenDef)
    {
        Doc = doc;
        ScreenDef = screenDef;
    }
}



List<MyItem> tmp = (from oScreenDef in listScreenDefinition
                    let oScreenDefVenueCd = oScreenDef["venueCd"]  // let clause creates a "local variable" Inside a LINQ query
                    join oSynSession in listSynSession on
                        new { c1 = oScreenDefVenueCd, c2 = oScreenDef["screenBytNum"] }
                        equals new { c1 = oSynSession["cinemaId"], c2 = oSynSession["screenDetails"].AsBsonDocument["num"] }
                    join oSessionAreaCount in listSessionAreaCount on
                        oScreenDefVenueCd
                        equals oSessionAreaCount["cinemaId"]
                    join oPrices in listSynPrices on
                        new { c1 = oScreenDefVenueCd, c2 = oSynSession["cinemaId"] }
                        equals new { c1 = oPrices["cinemaId"], c2 = oPrices["cinemaId"] }
                    select new MyItem(oSynSession[0], oScreenDef)).ToList();

rtpHarry update note: renamed Item to MyItem to match the class at the top.