. NET open source database design tool MR.E for LINQ (EF 6.1) tutorial (ii) cascading deletions and triggers

1. Establishing a cascade Delete

MR.E Cascade Delete is not a database with that cascade Delete, but MR.E comes with it, so it can trigger your C # written trigger.

First, establish a cascade delete relationship, such as two tables, userinfo and UserDocument,

The UserDocument table relies on the UserID field, which is associated with userinfo. Now I want to implement, when the data inside the UserInfo deleted, automatically delete the UserDocument table inside the userid=userinfo.id of those data, what should be done?

First, double-click UserInfo to open its property editor, click the Cascade Delete setting item, add a cascade delete relationship

Then compile the database DLL, we go to the code there to experiment.

2. Triggers

First create a new Userdocumentaction class, Inherit Entitydb.actioncapture<test.userdocument>, as a trigger for the UserDocument table

usingSystem;usingSystem.Collections.Generic;usingSystem.Diagnostics;usingSystem.Linq;usingSystem.Text;usingSystem.Threading.Tasks;namespacelinqtest1{ Public classUserdocumentaction:entitydb.actioncapture<test.userdocument>    {         Public Override voidBeforeInsert (Objectdatabase, Entitydb.databasemodifyeventarg e) {Debug.WriteLine ("userdocument BeforeInsert"); }         Public Override voidAfterInsert (Objectdatabase, Entitydb.databasemodifyeventarg e) {            vardata =(test.userdocument) E.dataitem; Debug.WriteLine (string. Format ("UserDocument found new data, id={0} filename={1}", Data.id, data.        FileName)); }         Public Override voidBeforeUpdate (Objectdatabase, Entitydb.databasemodifyeventarg e) {                    }         Public Override voidAfterUpdate (Objectdatabase, Entitydb.databasemodifyeventarg e) {                    }         Public Override voidBeforeDelete (Objectdatabase, Entitydb.databasemodifyeventarg e) {            vardb =(Test.DB.TestDB) database; vardata =(test.userdocument) E.dataitem; //data only has a value in the ID field, so to get all the values out of the field, you need to go to the database and fetch it once .data = db. Userdocument.firstordefault (M=>m.id = =data.id); Debug.WriteLine ("data is about to be deleted: Filename="+ data. FileName +"desc="+data.        DESC); }         Public Override voidAfterDelete (Objectdatabase, Entitydb.databasemodifyeventarg e) {Debug.WriteLine ("userdocument AfterDelete"); }    }}

Then write the code to insert the data, delete the data, and see if Userdocumentaction can capture the event correctly

usingSystem;usingSystem.Collections.Generic;usingSystem.ComponentModel;usingSystem.Data;usingSystem.Diagnostics;usingSystem.Drawing;usingSystem.Linq;usingSystem.Text;usingSystem.Threading.Tasks;usingSystem.Windows.Forms;namespacelinqtest1{ Public Partial classForm1:form { PublicForm1 () {InitializeComponent (); }        Private voidForm1_Load (Objectsender, EventArgs e) {            using(vardb =NewTest.DB.TestDB (@"data source= "" F:\SqliteLinqTest\TestDB """, EntityDB.DatabaseType.Sqlite)) {                //Start a transactiondb.                BeginTransaction (); Try                {                    //add userinfo table Data                    varuser =NewTest.userinfo (); User. UserName="Zhang San"; User. Password="123"; Db.                    Update (user); //add userdocument table Data                    varUserdoc =Newtest.userdocument (); Userdoc.userid=user.id; Userdoc.filename="d:\\ test document. doc"; Userdoc.desc="Test Document"; Db.                    Update (Userdoc); //Delete Userdb.                    Delete (user); //Commit a transactiondb.committransaction (); }                Catch                {                    //rolling back a transactiondb.                    RollbackTransaction (); Throw; }            }        }    }}

Run the code and discover the db. Delete (user); When the user's data is deleted, the cascade delete works, automatically deletes the data inside the userdocument , and is captured by the Userdocumentaction trigger.

. NET open source database design tool MR.E for LINQ (EF 6.1) tutorial (ii) cascading deletions and triggers