LINQ to SQL

LINQ is a language-integrated query instead of a database, which is more concise and easier to use than a database, of course, this is his advantage. His focus is on the query expression.
LINQ Query Expressions:
It consists of three main parts:
1. Get the data source
2. Create a query
3. Execute Query
Anonymous method:
Before 2.0, the only way to declare a delegate is to use a named method. Lambda expressions Replace anonymous methods in version 3.0 and later
Lambda expression:
1. What about him? An anonymous function that contains expressions and statements that can be used to create delegates
2. Lambda expression "X=>x * x" reads "x goes to X times X"
Query syntax and method statements:
We follow the three elements, first you need to have a data source.
String[] devices= {"TV", "refrigerator", "Washing machine", "telephone", "Microwave oven"};
Then there is the query syntax,
1. Select:
var selectdevices = from P in Devices
Select P;
And then there's a method statement with a forerch.
foreach (String dev in selectdevices)
{
Console.WriteLine ("The letter is: {0}", dev);
}
Here are some of the more complex query operations I think it's easy to write query statements if you learn LINQ from a database.
2. Where:
String[] devices= {"A", "B", "C", "D", "E"};
var selectdevices = from device in Devices
where P.startswith ("B")
Select P;
foreach (String dev in selectdevices)
{
Console.WriteLine ("The letter is: {0}", dev);
}
Or our three elements, is the same as the database in the middle of the inclusion of a Where condition
3.
String[] devices= {"A", "B", "C", "D", "E"};
var selectdevices = from P in Devices
where P.startswith ("B")
Select P;
foreach (String dev in selectdevices)
{
Console.WriteLine ("The letter is: {0}", dev);
}
4. Connection Query
Linqdbdatacontext db = new Linqdbdatacontext (linqsystem.linqdbconnectionstring);
var result = from the user in db. UserInfo
Join UR in db. userrole on user.id equals Ur. Userid
Join role in DB. Role on Ur. Roleid equals role.id
Where User.ID < 200
Select New {id = user.id,//display ID, user name, email address and role
UserName = user. Username,
Email = user. Email,
RoleName = role. RoleName
};
Dl_list.datasource = result;
Dl_list.databind ();

5. Aggregate Query
Linqdbdatacontext db = new Linqdbdatacontext (linqsystem.linqdbconnectionstring);
var result = from P in db. Product
Select p;//calculates the highest and lowest price of the item
Decimal Maxprice = result. Max (p = p.price.value);
Decimal Minprice = result. Min (p = p.price.value); Show highest and lowest prices
Response.Write (String. Format ("Maximum price: {0}, lowest price: {1}", Maxprice,minprice));
6. Group Query
Linqdbdatacontext db = new Linqdbdatacontext (linqsystem.linqdbconnectionstring);
var result = from P in db. Product
Group p by P.categoryid into G
G.key
Select New
{
Get product and category names
ProductName =g.first (). Name,
Catagoryname = (from u in db. Category
where U.id==g.key
Select U
). First (). Name
}; Data binding
Dl_list.datasource = result;
Dl_list.databind ();

Stored procedures:
1, add
Create proc pr_insertcategory (
@Name varchar () =null,
@ParentID int=null,
@ShowOrder Int=null,
@Remark text=null)
as
INSERT into Category ([Name],parentid,showorder,remark) values
(@Name, @ ParentID, @ShowOrder, @Remark)
Go
Adds the execution method:
String name = TextBox2.Text;
int id = Int. Parse (TextBox3.Text);
Tb_abc TB = new TB_ABC ()
{
Sname = name,
area_id = ID
};
Dc.tb_ABc.InsertOnSubmit (TB);
DC. SubmitChanges ();
Bind ();
Save more compact
Dc.p_addcreate (name,id);
bind ();
2. Delete
Create proc Deletecategroy
@ID int=null
as
Delete from Category where [email protected]
Go
Execution method for deletion:
(to invoke the "rowdeleting" event of the table)
String id = gridview1.datakeys[e.rowindex]. Value.tostring ();
var restr = from A in DC.TB_ABC
where a.sid.tostring () = = ID
Select A;
Dc.tb_ABc.DeleteAllOnSubmit (RESTR) ;
DC. SubmitChanges ();
Bind ();
Warm tip
: if (IsPostBack)
{
return;
}

LINQ to SQL