public void GeneralLinqToSql()
{
EmployeesDatabaseDataContext context =
new EmployeesDatabaseDataContext();
//
IQueryable<Employee> employees = from e in context.Employees
where e.JobDescription.JobDescription1 == "Developer"
orderby e.Name descending
select e;
IQueryable<Employee> employees2 = context.Employees.Where(e => e.JobDescription.JobDescription1 == "Developer")
.OrderByDescending(e => e.Name)
.Select(e => e); // Select is actually OPTIONAL
// Single selection
Employee employee1 = context.Employees.Where(e => e.JobDescription.JobDescription1 == "Developer")
.OrderByDescending(e => e.Name)
.Select(e => e)
.First(); // No corresponding keyword in comprehension syntax
}
public void LinqToAnonymousTypes()
{
EmployeesDatabaseDataContext context = new EmployeesDatabaseDataContext();
// var keyword has a key role
// Single selection
var employees1 = context.Employees.Where(e => e.JobDescription.JobDescription1 == "Developer")
.OrderByDescending(e => e.Name)
.Select(e => new
{
FirstName = e.Name
});
}
/// <summary>
/// Allows you to continue using a query after using Select.
/// </summary>
public void UsingInto()
{
EmployeesDatabaseDataContext context = new EmployeesDatabaseDataContext();
var output = from a in context.Employees
where a.Name == "David"
select a
into p
where p.Name.Length < 5
select p;
// Grouping
var output2 = from a in context.Employees
group a by a.JobDescriptionId into b
orderby b.Key ascending
select b;
// Composite Key grouping requires an anonymous type
var output3 = from a in context.Employees
group a by new
{
a.Name,
a.JobDescriptionId
};
}
/// <summary>
/// Let allows variables to be introduced into a query to help with reuse
/// </summary>
public void UsingLet()
{
EmployeesDatabaseDataContext context = new EmployeesDatabaseDataContext();
var output = from a in context.Employees
let lname = a.Name.ToLower()
where lname == "david"
select lname;
}
public void LinqToSqlSample()
{
EmployeesDatabaseDataContext context =
new EmployeesDatabaseDataContext();
IQueryable<Employee> employees = from e in context.Employees
where e.JobDescription.JobDescription1 == "Developer"
select e;
var output = employees.ToList();
}