How to write condition based on expression?-CodePudding

I am trying to write condition based on expression. I have two classes Test1 and Test2.

public class Test1<TEntity, TProperty>
{
    public IQueryable<TEntity> Test(
        IQueryable<TEntity> queryable,
        Expression<Func<TEntity, TProperty>> expression,
        TProperty value
    )
    {
        MemberExpression memberExpression = (MemberExpression)(expression.Body);
        var propName = memberExpression.Member.Name;

        // Cannot apply operator '>' to operands of type 'P' and 'P'
        queryable = queryable.Where(e => EF.Property<TProperty>(e, propName) > value));
        return queryable;
    }
}

public class Test2<TEntity, TProperty>
    where TProperty : IComparable
{
    public IQueryable<TEntity> Test(
        IQueryable<TEntity> queryable,
        Expression<Func<TEntity, TProperty>> expression,
        TProperty value
    )
    {
        MemberExpression memberExpression = (MemberExpression)(expression.Body);
        var propName = memberExpression.Member.Name;

        // This one compiles
        queryable = queryable.Where(e => EF.Property<TProperty>(e, propName).CompareTo(value) > 0);
        return queryable;
    }
}

First one (Test1) tries to compare values with > but it does not compile. Second one (Test2) declares generic type as IComparable and uses .CompareTo() method inside where condition. This one compiles but on runtime it throws:

The LINQ expression 'DbSet<SortableEntity>
    .Where(s => s.IsDeleted == False)
    .Where(s => EF.Property<long>((object)s, "Id").CompareTo((object)__value_0) > 0)' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync()

Is it possible to somehow write custom condition based on expression? I want property/member expression to be passed by user and then decide what condition to apply to IQueryable.

CodePudding user response：

Well, EF.Property is last thing that you have to use in such situation. You have property, even correct body - use this:

public class Test1<TEntity, TProperty>
{
    public IQueryable<TEntity> Test(
        IQueryable<TEntity> queryable,
        Expression<Func<TEntity, TProperty>> expression,
        TProperty value
    )
    {
        var predicateLambda = Expression.Lambda<Func<TEntity, bool>>(
            Expression.GreaterThan(expression.Body, Expression.Constant(value, typeof(TProperty))), 
            expression.Parameters[0]);

        queryable = queryable.Where(predicateLambda);
        return queryable;
    }
}