C# – Question about Northwind DB example

csubsonicsubsonic3

When messing with the Subsonic 3.0 Northwind stuff:

var product = Product.SingleOrDefault(x => x.ProductID == 1);

I found the following was possible, but not workable) using intellisense:

var product = Product.SingleOrDefault(x => x.OrderDetails == 1);

OrderDetails as a member of Product, is an IQueryable. I guess I'm new to LINQ, but I was wondering how to use this member? Everytime I try to get info out of this I get an error. Could someone give me an example of how to use the OrderDetails member of Product? And perhaps throw the results in a databind to a Gridview?

Look at the following code and tell me what I'm doing wrong:

 var products = from od in OrderDetail.All()
                   join p in Product.All() on od.ProductID equals p.ProductID
                   select od;

I get the following error:

Object of type 'System.Single' cannot be converted to type 'System.Decimal'.

Best Answer

The IQueriable members that are exposed by SubSonic are your Foreign Keys. You could use them in the following manner.

 Product.SingleOrDefault(x => x.ProductID == 1).OrderDetails.ToList()

Related Solutions

C# – What do two question marks together mean in C#

It's the null coalescing operator, and quite like the ternary (immediate-if) operator. See also ?? Operator - MSDN.

FormsAuth = formsAuth ?? new FormsAuthenticationWrapper();

expands to:

FormsAuth = formsAuth != null ? formsAuth : new FormsAuthenticationWrapper();

which further expands to:

if(formsAuth != null)
    FormsAuth = formsAuth;
else
    FormsAuth = new FormsAuthenticationWrapper();

In English, it means "If whatever is to the left is not null, use that, otherwise use what's to the right."

Note that you can use any number of these in sequence. The following statement will assign the first non-null Answer# to Answer (if all Answers are null then the Answer is null):

string Answer = Answer1 ?? Answer2 ?? Answer3 ?? Answer4;

Also it's worth mentioning while the expansion above is conceptually equivalent, the result of each expression is only evaluated once. This is important if for example an expression is a method call with side effects. (Credit to @Joey for pointing this out.)

C# – How To Define The Return Type In A Function With LINQ

You want to return IEnumerable<Product>, which represents an iterable (or enumerable) of objects of type Product. LINQ in general is all based around this generic type, so it's generally what you want to return as a result of a query.

I believe your code should be fixed to become something like this:

public static IEnumerable<Products> GetProducts(int pid) 
{
    var pro = from p in context.Products
              select p;

    if(pid > 0)
        pro =  pro.Where(p => p.ProductID == pid)

    return pro;
}

Let me know if you meant something else in your question. I wasn't totally sure what precisely you were searching for.

Best Answer

Related Solutions

C# – What do two question marks together mean in C#

C# – How To Define The Return Type In A Function With LINQ

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