Linq expression for field selection

Question

I have a very specific LINQ query. I would like to check for a randomly generated key in the table.

A standard query can be defined as Select * from Products where SaleId == 'XXXXXXX'. In this request, XXXXXX is generated by a random character generator (length is also provided). I created the following LINQ extension:

public static string GetUniqueId<T, TProperty>(this IEnumerable<T> source, int length, Func<T, TProperty> idProperty)
{
    bool isUnique = false;
    string uniqueId = String.Empty;
    while (!isUnique)
    {
        uniqueId = PasswordGenerator.GenerateNoSpecialCharacters(length);
        if (!String.IsNullOrEmpty(uniqueId))
        {
            isUnique = source.AsQueryable().SingleOrDefault(i => idProperty(i).Equals(uniqueId)) == null;
        }
    }
    return uniqueId;
}

However, I noticed that this method first selects all the records from the table, which is passed as the source, and then runs the Where clause. This behavior obviously takes a lot of time. So basically this SELECT * FROM Productsand then runs SingleOrDefault

Is there a way that I could directly run the query so that it selects * from the products WHERE Id = 'XXXXXXX'

Here is an example of what I call it:

string id = c.L2SOnlineCountMasters.GetUniqueId(9, x => x.MID);

L2SOnlineCountMasters c DataContext.

!

Cheerz, Anup

Answer 1

, , IQueryable . "Equals" Expression Call , : " " Equals " " System.String " ". , :

public static string GetUniqueId<T, TProperty>(this IQueryable<T> source, int length, Expression<Func<T, TProperty>> idProperty)
    {
        bool isUnique = false;
        string uniqueId = String.Empty;
        while (!isUnique)
        {
            uniqueId = PasswordGenerator.GenerateNoSpecialCharacters(length);
            if (!String.IsNullOrEmpty(uniqueId))
            {
                var expr = Expression.Lambda<Func<T, bool>>(
                    Expression.Call(idProperty.Body, typeof(string).GetMethod("Equals", new[] { typeof(string) }), Expression.Constant(uniqueId)), idProperty.Parameters);
                isUnique = source.SingleOrDefault(expr) == null;
            }
        }

        return uniqueId;
    }

.

Answer 2

LINQ to SQL , Func<T, TProperty>.

Expression<Func<T, TProperty>>, , .Equals.

Expression.Lambda<Func<T, TProperty>>(
    Expression.Call(idProperty.Body, "Equals", new Type[0], 
                    Expresion.Constant(uniqueId)),
    idProperty.Parameters
)

, , IQueryable<T>.

Answer 3

, , c.L2SOnlineCountMasters IEnumerable, :

    public static string GetUniqueId<T, TProperty>(this IQueryable<T> source, int length, Func<T, TProperty> idProperty)
{         
bool isUnique = false;         
string uniqueId = String.Empty;         
while (!isUnique) 
{             
uniqueId = PasswordGenerator.GenerateNoSpecialCharacters(length);             
if (!String.IsNullOrEmpty(uniqueId)) 
{ 
isUnique = source.SingleOrDefault(i => idProperty(i).Equals(uniqueId)) == null;
}
}
return uniqueId;
}