C#•14mo ago

❔ EF Core optional where extension method

I have a lot of optional parameters for queries. Filter by this, filter by that etc. I can do it like this context.table.Where(x => projectId == null || x.ProjectId == projectId) (This actually doesnt even add a WHERE TRUE to the generated SQL Query

would like to avoid the null check or part every time and write something like .OptionalWhere(x => x.ProjectId, projectId) but I cant find the correct syntax for the extension method. Im trying stuff similiar to this

public static IQueryable<T> OptionalWhere<T, T2>(this IQueryable<T> source, Expression<Func<T, T2>> selector, T2 value)
    {
        if (value == null)
            return source;

        return source.Where(x => selector.Compile()(x).Equals(value));
    }

public static IQueryable<T> OptionalWhere<T, T2>(this IQueryable<T> source, Expression<Func<T, T2>> selector, T2 value)
    {
        if (value == null)
            return source;

        return source.Where(x => selector.Compile()(x).Equals(value));
    }

Func cant be translated. Expression cant be translated if I compile it. I guess because it turns into a func..

public static IQueryable<TSource> WhereNotNull<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
    {
        // somehow look into the predicate whether its an equals clause and check if the "right side" is null and return source back
        return source.Where(predicate);
    }

public static IQueryable<TSource> WhereNotNull<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
    {
        // somehow look into the predicate whether its an equals clause and check if the "right side" is null and return source back
        return source.Where(predicate);
    }

6 Replies

Kiel•14mo ago

Expression.AndAlso() might be what you're looking for?

Kiel•14mo ago

https://stackoverflow.com/questions/457316/combining-two-expressions-expressionfunct-bool

Stack Overflow

Combining two expressions (Expression>)

I have two expressions of type Expression<Func<T, bool>> and I want to take to OR, AND or NOT of these and get a new expression of the same type Expression<Func<T, bool>> e...

Kiel•14mo ago

i think what you want to do is combine two expressions, one that's "hardcoded" (x != null) and the one passed in (selector)

Saber•14mo ago

I did something like this

public static IQueryable<T> WhereIf<T>(this IQueryable<T> queryable, bool condition, Expression<Func<T, bool>> func)
  => condition ? queryable.Where(func) : queryable;

public static IQueryable<T> WhereIfNotNull<T, U>(this IQueryable<T> queryable, U item, Expression<Func<T, bool>> func)
  => item != null ? queryable.Where(func) : queryable;

public static IQueryable<T> WhereIfNotEmpty<T>(this IQueryable<T> queryable, string item, Expression<Func<T, bool>> func)
  => !string.IsNullOrEmpty(item) ? queryable.Where(func) : queryable;

public static IQueryable<T> WhereIf<T>(this IQueryable<T> queryable, bool condition, Expression<Func<T, bool>> func)
  => condition ? queryable.Where(func) : queryable;

public static IQueryable<T> WhereIfNotNull<T, U>(this IQueryable<T> queryable, U item, Expression<Func<T, bool>> func)
  => item != null ? queryable.Where(func) : queryable;

public static IQueryable<T> WhereIfNotEmpty<T>(this IQueryable<T> queryable, string item, Expression<Func<T, bool>> func)
  => !string.IsNullOrEmpty(item) ? queryable.Where(func) : queryable;

MaskoeOP•14mo ago

yea but these barely gain anything in being more concise, if its now 2 arguments in the method, instead of 2 conditions in the where clause .WhereIfNotNull(myId, x => x.Id == myId) vs .Where(x => myId == null || x.Id == myId)

Accord•14mo 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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❔ EF Core optional where extension method