Exploratory work on custom aggregate methods #1531
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roji
commented
Oct 11, 2020
| return AggregateResultShaper(source, projection, throwWhenEmpty: true, typeof(string)); | ||
| } | ||
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| #region Copied from RelationalQueryableMethodTranslatingExpressionVisitor |
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Note code copied below, which seems like it would be necessary for anyone needing to add top-level aggregate function support. Ideally this duplication wouldn't be necessary.
roji
commented
Oct 11, 2020
| @"@__p_1='|' | ||
| @__p_0='2' | ||
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| SELECT string_agg(t.""ContactName"", @__p_1) |
roji
commented
Oct 11, 2020
| var lambdaBody = ReplacingExpressionVisitor.Replace( | ||
| lambdaExpression.Parameters.Single(), shapedQueryExpression.ShaperExpression, lambdaExpression.Body); | ||
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| // TODO: Can't duplicate WeakEntityExpandingExpressionVisitor (ColumnExpression ctors are internal) |
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Apparently not possible support weak entities
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Following discussion in dotnet/efcore#13278, I attempted to translate string_agg, which is a PostgreSQL-specific aggregate function that reduces a set of values to a single string (concatenation). There are some other similar functions.
I did successfully managed to translate top-level (IQueryable) invocations, which is really cool. However, the current query pipeline doesn't seem to allow custom functions in the GroupBy aggregate case (e.g. GroupingElementExpression is private). Assuming we want to fully support arbitrary aggregate functions, we can use this to understand what's needed.
/cc @smitpatel @ajcvickers