如何在linq实体框架c#中使用和if语句

Question

I am declaring this variable to get data from my database(example)

var products = _context.Products();

and I need to use like this example

if(ctId == -1)
{
    // get project list 
    var products = _context.Products().where(a => a.categoryId == 2);
}
else
{
    //get category list
    var products = _context.Products().where(a => a.categoryId == 1);
}

but my problem how to declare var products to using like this

if(ctId == -1)
{
    // get project list 
    products = _context.Products().where(a => a.categoryId == 2);
}
else
{
    //get category list
    products = _context.Products().where(a => a.categoryId == 1);
}

Answer 1

To the initial problem, you would declare an IQueryable<Product> outside the if scope

IQueryable<Product> products = null;

if(ctId == -1)
   products = _context.Products().where(a => a.categoryId == 2);
else
   products = _context.Products().where(a => a.categoryId == 1);

However, you could also use a ternary conditional operator

The conditional operator ?: , also known as the ternary conditional operator , evaluates a Boolean expression and returns the result of one of the two expressions, depending on whether the Boolean expression evaluates to true or false .

The syntax for the conditional operator is as follows:

 condition ? consequent : alternative

Example

var id = ctId == -1 ? 2 : 1;
var products = _context.Products().where(a => a.categoryId == id);

or potentially

var products = _context.Products().where(a => a.categoryId == (ctId == -1 ? 2 : 1));