c# - LINQ: adding where clause only when a value is not null

Question

I know a typical way is like this:

IQueryable query = from staff in dataContext.Staffs;
if(name1 != null)
{
     query = from staff in query where (staff.name == name1);
}

However, from a program we took over from other developers, we saw code like this:

IQueryable query = from staff in dataContext.Staffs;
query = from staff in query where (name1 == null || staff.name == name1);

If this is a normal SQL statement, I would definitely say that the 2nd one is a bad practice. Because it adds a meaningless where clause to the query when name1 is null.

But I am new to LINQ, so I am not sure if LINQ is different?

Answer 1

you can write it like

IQueryable query = from staff in dataContext.Staffs;
query = from staff in query where (name1 != null && staff.name == name1);

This way second part of your condition will not be evaluated if your first condition evaluates to false

Update:
if you write

IQueryable query = from staff in dataContext.Staffs;
    query = from staff in query where (name1 == null || staff.name == name1);

and name1 is null second part of your condition will not be evaluated since or condition only requires one condition to return true

plz see this link for further detail