EF Core dynamic filter on boolean column - entity-framework-core

Question

I want to apply a filter on boolean column which I will get it from the frontend as a parameter. It may be true, false or both. I can use the if statement to run the query but I need to add other methods like Take, Skip, OrderBy etc., which I have removed it for brevity. Is there any way to build the dynamic expression for below condition
if(parameter == "true")
_db.Employees.Where(e => e.Status = true)
else if (parameter == "false")
_db.Employees.Where(e => e.Status = false)
else
_db.Employees.ToList() //Return both true and false

Answer 1

LINQ queries are already dynamic. Every LINQ operator returns a new IQueryable<> query. You can construct a query bit by bit based on various conditions this way, eg :
var query=db.Employees.AsQueryable();
if(status=="Active")
{
query=query.Where(e=>e.Active);
}
if(dateAscending)
{
query=query.OrderBy(e=>e.Date);
}
if(page==1)
{
query=query.Take(pageSize);
}
else
{
query=query.Skip(page*pageSize).Take(pageSize);
}
...
var employees=await query.ToListAsync();
The tricky part is handling NULLs. In SQL, NULL means there's no value and any comparison with NULL returns NULL itself, which is translated as false. If Status or Active are nullable, you can't return any rows with NULLs by comparing with false. You'll have to compare with null explicitly. EF Core translates that to IS NULL.
Using a switch expression you can combine the various Status checks with this:
query = (status) switch
{
"true" => query.Where(e=>e.Status),
"false" => query.Where(e=>!e.Status),
"both" => query.Where(e=> e.Status !=null)
_ => query.Where(e=>e.Status == null)
};
This expression assumes that an empty string is meant to match NULLs. both means retrieving TRUE and FALSE but not NULL.
If don't care about NULLs, this can be simplified to :
query = (status) switch
{
"true" => query.Where(e=>e.Status),
"false" => query.Where(e=>!e.Status),
_ => query
};