Query: Apply CompositePredicateExpressionVisitor to join predicates

[smitpatel]

At present it is applied to SelectExpression.Predicate only

[maumar]

Also add more optimizations, e.g. ((c.Discriminator == "Foo" ? c.FK : null) == o.PK into c.Discriminator == "Foo" && c.FK == o.PK)

[ajcvickers]

@maumar @smitpatel Please update description with more details and investigate for 2.1.

[smitpatel]

Derived Include generates join condition using ternary to appropriately cast to derived type.
Which generates query like this

SELECT [l].[Name], [l].[Discriminator], [l].[LocustHordeId], [l].[ThreatLevel], [l].[DefeatedByNickname], [l].[DefeatedBySquadId], [t].[Nickname], [t].[SquadId], [t].[AssignedCityName], [t].[CityOrBirthName], [t].[Discriminator], [t].[FullName], [t].[HasSoulPatch], [t].[LeaderNickname], [t].[LeaderSquadId], [t].[Rank]
FROM [LocustLeaders] AS [l]
LEFT JOIN (
    SELECT [l.DefeatedBy].*
    FROM [Gears] AS [l.DefeatedBy]
    WHERE [l.DefeatedBy].[Discriminator] IN (N'Officer', N'Gear')
) AS [t] ON (CASE
    WHEN [l].[Discriminator] = N'LocustCommander'
    THEN [l].[DefeatedByNickname] ELSE NULL
END = [t].[Nickname]) AND (CASE
    WHEN [l].[Discriminator] = N'LocustCommander'
    THEN [l].[DefeatedBySquadId] ELSE NULL
END = [t].[SquadId])
WHERE [l].[Discriminator] IN (N'LocustCommander', N'LocustLeader')

Here using Case block on join condition means join cannot use any index and no longer sargable.

[maumar]

fixed in 9355f64