The EF Framework's operations on the database

Web-based database operations:

Traditional method: ADO

Query, modify, delete, and insert new records by calling SQL statements from an ADO object.

New method: EF

Converts a traditional database into an object-oriented entity (entity) and becomes the definition of a class (database counterpart, traditional table Table object)

Microsoft offers: EntityFramework for short, EF

Entity Framework

Benefits of EF:

Avoid mixing SQL syntax with C # syntax;

All use visual object-oriented syntax.

There are real-time code hints.

Two ways to model database:

Db-first a database first, then a model

(generally using Db-first)

Code-first is modeled first, and then the database is generated according to the model.

Xsdbentities mydb = new Xsdbentities ();

Generates an object for the entity class MyDB

Xsbasetable Myrecord = Mydb.xsBASETABLE.First (); Find the first record

Generate a record of the student base table corresponding to the record to be deleted

Mydb.xsBASETABLE.Remove (Myrecord); Delete a specified record in a model

MyDB. SaveChanges ();

Saves the operation of the model to SQL Server.

protected void Button1_Click (object sender, EventArgs e)

{

Add a record

Xsdbentities mydb = new Xsdbentities ();

Xsbasetable Myrecord = new Xsbasetable () {xh= "004", Name= "dddd", address= "one 101"};

Create a record of a new table and assign a value directly after the constructor

MYDB.XSBASETABLE.ADD (Myrecord);

To add a new record to the model

MyDB. SaveChanges ();

Saves the operation of the model to SQL Server.

}

protected void Button3_Click (object sender, EventArgs e)

{

Modify a record

Xsdbentities mydb = new Xsdbentities (); New Entity Object

Xsbasetable Myrecord = Mydb.xsBASETABLE.First (); Find the first record

Myrecord.xh = "008"; Modify each field of the record

Myrecord.name = "Liming";

myrecord.address = "Four building 201";

MyDB. SaveChanges ();

Saves the operation of the model to SQL Server.

}

protected void Button4_Click (object sender, EventArgs e)

{//Query code

Xsdbentities mydb = new Xsdbentities (); Generating Entity objects

Xsbasetable Myrecord = Mydb.xsBASETABLE.First (); Find the records you need

This.  TextBox1.Text = Myrecord.name; Assign a field of this record to a text box

}

protected void Button4_Click (object sender, EventArgs e)

{

Code that queries any condition

Xsdbentities mydb = new Xsdbentities (); Generating Entity objects

var Myrecord = mydb.xsbasetable.

Where (c = c.xh = = "005" && c.name= "dddd");

Find a collection of records that meet the criteria

var stands for any type of variable

This. TextBox1.Text = Myrecord. FirstOrDefault (). Name;

Assigns a field from the first record in a record collection that satisfies a condition to a text box

}

Multiple record deletions:

Xsdbentities mydb = new Xsdbentities ();

VAR[U1] myrecord[u2] = Mydb.xsBASETABLE.Where (N[u3] =>[u4] n.xh==[u5] "004"); Find a collection that satisfies a condition record

foreach (var temp in Myrecord)//iterate over each object in the collection

{

Mydb.xsBASETABLE.Remove (temp); Delete a specified record in a model

}

MyDB. SaveChanges ();

Saves the operation of the model to SQL Server.

[U1] represents any data type.

The Var a=3 computer knows that a is an integral type.

[U2] Variable collection

[U3] Any variable name

[U4] Lambda expression

[U5] is a C language sentence.

The EF Framework's operations on the database