C#•10mo ago

❔ How can I make a function of a simple condition EF Core translatable

Hey, so I have this function, but it seems to throw an error by not being translatable by EF Core, even though if the code is extracted from the function, it seems to work just fine. Function that cannot be translated:

public static bool IsWithinRange(this DateTime target, DateTime rangeStart, DateTime rangeEnd)
        => target >= rangeStart && target <= rangeEnd;

public static bool IsWithinRange(this DateTime target, DateTime rangeStart, DateTime rangeEnd)
        => target >= rangeStart && target <= rangeEnd;

But this is fine:

.Where(x => x.Timestamp >= _startDate && x.Timestamp <= _endDate)

.Where(x => x.Timestamp >= _startDate && x.Timestamp <= _endDate)

Can anyone explain how I can fix that?

16 Replies

Pobiega•10mo ago

Yep! Functions are not translatable to SQL, but expression are check the types on Where there

Rese•10mo ago

Okay, I did try to form it into an expression and it also didn't seem to work. I'm assuming I'm just calling it wrong since there are multiple parameters. Expression:

public Expression<Func<DateTime, DateTime, DateTime, bool>> IsWithinRangeExpr =
        (target, rangeStart, rangeEnd) => target >= rangeStart && target <= rangeEnd;

public Expression<Func<DateTime, DateTime, DateTime, bool>> IsWithinRangeExpr =
        (target, rangeStart, rangeEnd) => target >= rangeStart && target <= rangeEnd;

Call:

.Where(x => IsWithinRangeExpr.Compile()(x.Timestamp, _startDate, _endDate))

.Where(x => IsWithinRangeExpr.Compile()(x.Timestamp, _startDate, _endDate))

Throws the same error As in not translatable Or is it that I can't call compile and therefore use those other arguments?

Pobiega•10mo ago

that compile is definately not right hang on a sec

Rese•10mo ago

yeah it didn't look right to me either 😄

Pobiega•10mo ago

I'd probably recommend just not using a function and baking it into your query. It will be a lot more readable that way :p

Rese•10mo ago

The reason why I wanna do it this way is because it's part of a more complicated query, which would just clutter the code a lot. But that one is definitely possible to be translatable by EF Core once this issue is resolved

Pobiega•10mo ago

you can make a dynamic expression, but it might be a bit messy

Rese•10mo ago

what does that mean? Like wasn't the above example that?

Pobiega•10mo ago

something like this

Pobiega•10mo ago

https://stackoverflow.com/questions/61412241/build-expression-to-filter-data-ef-core

Stack Overflow

Build Expression to filter data EF Core

I need to reuse available expression: Expression<Func<Picture, int>> selector = o => o.EntityId; And build expression for Where: Expression<Func<Picture, bool>> filter...

Rese•10mo ago

Well that just looks miserable 😄

Pobiega•10mo ago

exactly

Rese•10mo ago

So there's no other way? Essentially EF Core can't parse the method itself even if it is a function with content that would be translatable?

Pobiega•10mo ago

Thats correct. EF can only translate expressions There might be a better way to make that expression method, but I'm far from an expert at this

Angius•10mo ago

The expression has to be the same as the lambda the method takes So if it's a Things.Where(x => x.Stuff > 10) you need

Expression<Func<Thing, bool>> Boo = (Thing t) => t.Stuff > 10;

Expression<Func<Thing, bool>> Boo = (Thing t) => t.Stuff > 10;

and you can call

Things.Where(Boo)

Things.Where(Boo)

So an expression like

public Expression<Func<Thing, bool>> IsWithinRangeExpr
  = (t) => t.Target >= t.RangeStart && t.Target <= t.RangeEnd;

public Expression<Func<Thing, bool>> IsWithinRangeExpr
  = (t) => t.Target >= t.RangeStart && t.Target <= t.RangeEnd;

might work

Accord•10mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ How can I make a function of a simple condition EF Core translatable