Overload for LINQ List.Contains() to accept column name

Question

I would like to modify the following procedure

        public async Task<IActionResult> GetMany(List<int> values)
        {
             List<TEntity> entities = await _crudApiDbContext.Set<TEntity>()
                    .Where(entity => values.Contains(entity.Id)).ToListAsync();
             return new OkObjectResult(entities);
        }

to accept the column name which will be searched in the Contains method, something like:

        public async Task<IActionResult> GetMany(List<int> values, string colName)
        {
             List<TEntity> entities = await _crudApiDbContext.Set<TEntity>()
                    .Where(entity => values.Contains<TEntity>(colName)).ToListAsync();
             return new OkObjectResult(entities);
        }

I've tried overloading Contains and using expression trees but got lost...

Any ideas?

Answer 1

Introduce the following extension method, which should filter any entity type by collection:

public static class QueryableExtensions
{
    public static IQueryable<TEntity> FilterByList<TEntity, TKey>(this IQueryable<TEntity> query, IEnumerable<TKey> values, string colName) 
        where TEntity : class
    {
        var param = Expression.Parameter(typeof(TEntity), "e");
        var propAccess = Expression.PropertyOrField(param, colName);
        var listExpr = Expression.Constant(values);

        var predicate = Expression.Call(typeof(Enumerable), "Contains", new[] {typeof(TKey)}, listExpr,
            propAccess);

        var predicateLambda = Expression.Lambda<Func<TEntity, bool>>(predicate, param);

        return query.Where(predicateLambda);
    }
}

And rewrite your GetMany to this variant:

public async Task<IActionResult> GetMany<TEntity>(List<int> values, string colName)
{
    var entities = await _crudApiDbContext.Set<TEntity>()
        .FilterByList(values, colName)
        .ToListAsync();
    return new OkObjectResult(entities);
}