Create an empty Expression <Func>

Question

I'm working on a .NET Core WebApi project using the Repository pattern and I'm having troubles implementing a solution for a certain case:

This is my Controller method where I'm passing a variable called name, which I will use to create an expression for a LINQ query

public async Task<ActionResult<ActivityDto>> GetPaginated(int page, int size, string name)
{
    var entities = await _activityService.GetPaginatedActivitiesAsync(page, size, name);

    if (!entities.Any())
        return NotFound();

    return new ObjectResult(entities) { StatusCode = StatusCodes.Status200OK };
}

I also have this piece of code in a method in my Service layer, where I use to create the certain expression, and then call my Repository method which will execute a certain query.

Expression<Func<Activity, bool>> filter = u => u.Name.Equals(name);
var entities = await _activityRepository.GetPaginatedAsync(page, size, filter);

This is the line in my Repository, where I execute the query, which returns all the recourds based on the input name.

await _context.Set<TEntity>().Where(filter).ToListAsync();

This all code works fine for the case when I pass a certain string to the name variable in the Controller. The thing is I'm supposed to check if the user inputs any string for the name field, and if not to return all the records. So my question is : Is there any way to create something like an Empty Expression, which then will be executed by the LINQ Query?

Answer 1

You can use a Func returning true:

Expression<Func<Activity, bool>> filter = u => true;

But I would say that possibly better approach is to pass null value for filter and check it inside GetPaginatedAsync like that:

IQueryable<TEntity> query = _context.Set<TEntity>();
if (filter != null)
{
    query = query.Where(filter);
}

await query.ToListAsync();