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Sequence Operators (LINQ to SQL)

  • Artykuł

Generally speaking, LINQ to SQL does not support sequence operators that have one or more of the following qualities:

  • Take a lambda with an index parameter.

  • Rely on the properties of sequential rows, such as TakeWhile.

  • Rely on an arbitrary CLR implementation, such as IComparer<T>.

Examples of Unsupported

Enumerable.Where<TSource>(IEnumerable<TSource>, Func<TSource, Int32, Boolean>)

Enumerable.Select<TSource, TResult>(IEnumerable<TSource>, Func<TSource, TResult>)

Enumerable.Select<TSource, TResult>(IEnumerable<TSource>, Func<TSource, TResult>)

Enumerable.TakeWhile<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>)

Enumerable.TakeWhile<TSource>(IEnumerable<TSource>, Func<TSource, Int32, Boolean>)

Enumerable.SkipWhile<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>)

Enumerable.SkipWhile<TSource>(IEnumerable<TSource>, Func<TSource, Int32, Boolean>)

Enumerable.GroupBy<TSource, TKey, TElement>(IEnumerable<TSource>, Func<TSource, TKey>, Func<TSource, TElement>, IEqualityComparer<TKey>)

Enumerable.GroupBy<TSource, TKey, TElement, TResult>(IEnumerable<TSource>, Func<TSource, TKey>, Func<TSource, TElement>, Func<TKey, IEnumerable<TElement>, TResult>, IEqualityComparer<TKey>)

Enumerable.Reverse<TSource>(IEnumerable<TSource>)

Enumerable.DefaultIfEmpty<TSource>(IEnumerable<TSource>, TSource)

Enumerable.ElementAt<TSource>(IEnumerable<TSource>, Int32)

Enumerable.ElementAtOrDefault<TSource>(IEnumerable<TSource>, Int32)

Enumerable.Range(Int32, Int32)

Enumerable.Repeat<TResult>(TResult, Int32)

Enumerable.Empty<TResult>()

Enumerable.Contains<TSource>(IEnumerable<TSource>, TSource)

Enumerable.Aggregate<TSource>(IEnumerable<TSource>, Func<TSource, TSource, TSource>)

Enumerable.Aggregate<TSource, TAccumulate>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>)

Enumerable.Aggregate<TSource, TAccumulate, TResult>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>, Func<TAccumulate, TResult>)

Enumerable.SequenceEqual

Differences from .NET

All supported sequence operators work as expected in the common language runtime (CLR) except for Average. Average returns a value of the same type as the type being averaged, whereas in the CLR Average always returns either a Double or a Decimal. If the source argument is explicitly cast to double / decimal or the selector casts to double / decimal, the resulting SQL will also have such a conversion and the result will be as expected.

See Also

Other Resources

Data Types and Functions (LINQ to SQL)