There is nothing like LINQ for Java. … Edit Now with Java 8 we are introduced to the Stream API, this is a similar kind of thing when dealing with collections, but it is not quite the same as Linq. If it is an ORM you are looking for, like Entity Framework, then you can … Read more
I would use First() when I know or expect the sequence to have at least one element. In other words, when it is an exceptional occurrence that the sequence is empty. Use FirstOrDefault() when you know that you will need to check whether there was an element or not. In other words, when it is … Read more
You can’t query against the DataTable‘s Rows collection, since DataRowCollection doesn’t implement IEnumerable<T>. You need to use the AsEnumerable() extension for DataTable. Like so: var results = from myRow in myDataTable.AsEnumerable() where myRow.Field<int>(“RowNo”) == 1 select myRow; And as @Keith says, you’ll need to add a reference to System.Data.DataSetExtensions AsEnumerable() returns IEnumerable<DataRow>. If you need … Read more
Use an anonymous type. Eg group x by new { x.Column1, x.Column2 }
Yes, both will give you deferred execution. The difference is that IQueryable<T> is the interface that allows LINQ-to-SQL (LINQ.-to-anything really) to work. So if you further refine your query on an IQueryable<T>, that query will be executed in the database, if possible. For the IEnumerable<T> case, it will be LINQ-to-object, meaning that all objects matching … Read more
Absolutely – you basically want: var results = from p in persons group p.car by p.PersonId into g select new { PersonId = g.Key, Cars = g.ToList() }; Or as a non-query expression: var results = persons.GroupBy( p => p.PersonId, p => p.car, (key, g) => new { PersonId = key, Cars = g.ToList() }); … Read more
SelectMany flattens queries that return lists of lists. For example public class PhoneNumber { public string Number { get; set; } } public class Person { public IEnumerable<PhoneNumber> PhoneNumbers { get; set; } public string Name { get; set; } } IEnumerable<Person> people = new List<Person>(); // Select gets a list of lists of phone … Read more
What if I want to obtain a distinct list based on one or more properties? Simple! You want to group them and pick a winner out of the group. List<Person> distinctPeople = allPeople .GroupBy(p => p.PersonId) .Select(g => g.First()) .ToList(); If you want to define groups on multiple properties, here’s how: List<Person> distinctPeople = allPeople … Read more
This should work for you: var movies = _db.Movies.OrderBy(c => c.Category).ThenBy(n => n.Name)