Introduction:
- Linq is not c#3.0 and vice versa.
- New language enhancement introduced in c#
- Allow you to write structured type-safe queries over local object collections and remote data sources.
- The basic units of linq are sequence and elements
- Sequence- object implements the generic IEnumerable interface, Element-Each item in a sequence
Example:
int[]
valu = new int[]
{10,20,30};
here the valu is a sequence and 10,20,30 are elements.
Query operator:
Query operator is a method.
IEnumerable<string>
result = Enumerable.Where(stringarray, o =>
o.Length == 3);
"Where" is the query operator.
Two Types of Queries in linq:
- Comprehensive
- Lamda
Comprehension queries:
Comprehensive queries are syntactically same like sql queries but the executions
flows are different.
int[]
array = new int[7]
{ 0, 1, 2, 3, 4, 5, 6 };
var query = (from
no in
array
where (no % 3 == 0)
select no).ToArray();
foreach (int
no in
query)
{
Console.WriteLine(no);
}
Lamda Queries:
string[]
stringarray = { "How",
"are",
"you"
};
IEnumerable<string>
result = Enumerable.Where(stringarray,
o => o.Length == 3);
foreach
(string
res in
result)
Console.WriteLine(res);
(or)
string[]
stringarray = { "How",
"are",
"you"
};
IEnumerable<string>
result = stringarray.Where(stringarray,
o => o.Length == 3);
foreach
(string
res in
result)
Console.WriteLine(res);
Lamda queries are faster than comprehensive because internally comprehensive
queries are converted to lamda queries and executed ahead.
string[]
stringarray = { "Hi",
"How", "are",
"you","a"
};
IEnumerable<string>
result = stringarray
.Where(n => n.Contains("a"))
.OrderBy(n => n.Length)
.Select(n => n.ToUpper());
foreach (string
i in result)
Console.Write(i + ",");
Where, OrderBy, Select - Query operators
Execution start from left to right.
Mixing lamda and comprehensive queries:
In same query we can integrate comprehensive and lamda queries.
string[]
stringarray = { "Hi",
"How", "are",
"you","a"
};
int c = (from
n in stringarray
where stringarray.Contains("a")
select n).Count();
Console.WriteLine(c);