Question

I am reading records from database and check some conditions and store in List<Result>. Result is a class. Then performing LINQ query in List<Result> like grouping, counting etc. So there may be chance that min 50,000 records in List<Result>, so in this whether its better to go for LINQ (or) reinsert the records to db and perform the queries?

Answer 1

Why not store it in an IQueryable instead of a List and using LINQ to SQL or LINQ to Entities, the actual dataset will never be pulled into memory, and the queries will actually go down to the database to run.

Example:

Database db = new Database(); // this is what L2E gives you...

var children = db.Person.Where(p => p.Age < 21); // no actual database query performed


// will do : "select count(*) from Person where Age < 21"
int numChildren = children.Count();

var grouped = children.GroupBy(p => p.Age); // no actual query

int youngest = children.Min(p => p.Age); // performs query

int numYoungest = youngest.Count(p => p.Age == youngest); // performs query.

var youngestNames = children.Where(p => p.Age == youngest).Select(p => p.Name); // no query

var anArray = youngestNames.ToArray(); // performs query

string names = string.join(", ", anArray); // no query of course