Select is a LINQ functionality to define a data format of the query results.
Each of below examples is presented in C# with both Lambda and Query expression.
Let’s create a Person class.
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public class Person
{
public string Forename { get; set; }
public string Surname { get; set; }
public DateTime DateOfBirth { get; set; }
}
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And collection of people which we query with LINQ expressions.
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var people = new List<Person>()
{
new Person()
{
Forename = “John”,
Surname = “Smith”,
DateOfBirth = new DateTime(1980, 6, 14)
},
new Person()
{
Forename = “Bob”,
Surname = “Williams”,
DateOfBirth = new DateTime(1974, 2, 21)
},
new Person()
{
Forename = “Chris”,
Surname = “Jones”,
DateOfBirth = new DateTime(1990, 10, 4)
}
};
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1. Select single value
Query collection to get forenames only.
Lambda expression:
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var items = people.Select(x => x.Forename);
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Query expression:
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var items = from p in people
select p.Forename;
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Print to screen:
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foreach (var item in items)
Console.WriteLine(item);
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Result:
2. Select anonymous type
Query collection to get anonymous type objects containing surname and year of birth.
Lambda expression:
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var items = people.Select(
x => new
{
Surname = x.Surname,
YearOfBirth = x.DateOfBirth.Year
}
);
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Query expression:
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var items = from p in people
select new
{
Surname = p.Surname,
YearOfBirth = p.DateOfBirth.Year
};
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Print to screen:
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foreach (var item in items)
Console.WriteLine(item.Surname + “, “ + item.YearOfBirth);
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Result:
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Smith, 1980
Williams, 1974
Jones, 1990
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3. Select existing type
Query collection to get Person objects with upper-cased forenames and surnames.
Lambda expression:
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var items = people.Select(
x => new Person()
{
Forename = x.Forename.ToUpper(),
Surname = x.Surname.ToUpper(),
DateOfBirth = x.DateOfBirth
}
);
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Query expression:
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var items = from p in people
select new Person()
{
Forename = p.Forename.ToUpper(),
Surname = p.Surname.ToUpper(),
DateOfBirth = p.DateOfBirth
};
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Print to screen:
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foreach (var item in items)
Console.WriteLine(item.Forename + ” “ + item.Surname);
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Result:
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JOHN SMITH
BOB WILLIAMS
CHRIS JONES
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