Entity Framework Core - 附加条件 where 子句

Question

I am trying to add an additional where clause if a specific queryParameter is passed in through the url, but it doesn't seem to be working. Before I result to doing raw sql, I want to first figure out if I'm doing it correct (documentation seems to be minimal for this as I can't find anything)

Code minimized for brevity

public IActionResult RetrieveAll([FromQuery] string orderByDate, [FromQuery] string taskStatus)
{
    try
    {
        var taskQuery = (from t in _context.Tasks select t);
        switch(taskStatus)
        {
            case "completed":
                taskQuery.Where(t => t.IsCompleted == true);
                break;
            case "notcompleted":
                taskQuery.Where(t => t.IsCompleted == false);
                break;
        }

        var tasks = taskQuery.ToList();
        return Ok(tasks);
    }
    catch (Exception ex)
    {
        return BadRequest();
    }

}

I was thinking that simply appending the Where clause would do it. The code executes the proper code path, but It still comes back with all results.

Answer 1

You define the base query here:

var taskQuery = (from t in _context.Tasks select t);

Later, you call the .Where(...) extension method on the query in order to further filter the query:

 case "completed":
        taskQuery.Where(t => t.IsCompleted == true);
        break;

However, .Where(...) doesn't replace the IQueryable , it returns a new IQueryable . As you noted in the comments, you need to replace the query with the new query so that your call to .ToList() returns the expected results later.

Like this:

taskQuery = taskQuery.Where(t => t.IsCompleted == true);

That's a pretty common pattern for "building up" queries in Entity Framework, so you're definitely on the right track!