Check out example codes for "create expression func c# for use in where clause". It will help you in understanding the concepts better.

Code Example 1

private Expression<Func<PageElement, bool>> ActiveLanguageCheck(byte lang) {
    return pe => pe.PageElementLanguages.Where(
                    y => y.Active).Select(y => y.LanguageId).Contains(lang);
}

Code Example 2

public static Expression<Func<T1, TResult>> ToSimpleFunc<T1, T2, TResult>(Expression<Func<T1, T2, TResult>> f, T2 value)
{
    var invokeExpression = Expression.Invoke(f, f.Parameters[0], Expression.Constant(value));
    return Expression.Lambda<Func<T1, TResult>>(invokeExpression, f.Parameters[0]);
}

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