Java EE Learning Note hibernate03: Multi-table operations, cascading exercises: adding contacts

One or one-to-many | Many-to-one

1. Relationship Expression

Expression in the table

　　

Expression in an entity

　　

Expression in ORM Metadata

One-to-many

        <!--collections, one-to-many relationships, configuring in configuration Files -        <!--Name property: Collection Property Name column property: Foreign key Column Name Class Property: The full class name of the object associated with me -        <Setname= "Linkmens"Inverse= "true"Cascade= "Delete"  >            <Keycolumn= "lkm_cust_id" ></Key>            <One-to-manyclass= "Linkman" />        </Set>

Many-to-one

        <!---        <!--             Name property: Reference Property name            Column property: Foreign key Column Name            class Property: Object associated with me full class         name--         <name= "Customer" column = "lkm_cust_id" class = "Customer"  >        </ Many-to-one >

2. Operation

Action Association Properties

        //3 OperationCustomer C =NewCustomer (); C.setcust_name ("Wisdom Podcast"); Linkman LM1=NewLinkman (); Lm1.setlkm_name ("Lai Live Ming"); Linkman lm2=NewLinkman (); Lm2.setlkm_name ("Liuyueying East"); //Express one-to-many clients with multiple contactsC.getlinkmens (). Add (LM1);                C.getlinkmens (). Add (LM2); //To express to the right , to which customer the contact belongs.Lm1.setcustomer (c);                        Lm2.setcustomer (c);        Session.save (c);        Session.save (LM1); Session.save (LM2);

3. Advanced operation

　　Cascade Operations

         <!--               Cascade Operations:    Cascade                 save-update: Cascade Save update                 Delete: Cascade delete                 All:save-update+delete             cascade operations: Simplify the operation. The goal is to have less than two          lines of code. - 

        <set name= "Linkmens"  Inverse= "true"  Cascade= "delete" > <key column=" lkm_cust_id "></key> <one-to-many class< Span style= "COLOR: #0000ff" >= "Linkman" /> </set>        

Conclusion: Simplify the operation. Be sure to use, save-update, delete is not recommended.

Relationship Maintenance

　　

On save. Two parties maintain foreign key relationships. Relationship Maintenance two times, redundant. Redundant maintenance relationship statements, apparently the customer is maintaining the relationship at the end of the

          <!--Inverse property: Configures whether the relationship is maintained.              True:customer does not maintain relationship false (default): Customer maintains relationship inverse property: performance optimization. Improve the performance of relationship maintenance.              Principle: No matter how to give up, there must always be a party to maintain the relationship.          In a one-to-many relationship: a party gives up. Only one side can give up. Many of the parties cannot give up.  -        <Setname= "Linkmens"Inverse= "true"Cascade= "Delete"  >            <Keycolumn= "lkm_cust_id" ></Key>            <One-to-manyclass= "Linkman" />        </Set>

Two, many-to-many

1. Relationship Expression

Expression in the table

Object in

　　

ORM Meta-Data

        <!--Many-to-many relationship expressions -        <!--Name: Collection Property Name table: Configure the intermediate table name key |-column: Foreign Key, others refer to the Foreign key column name of "I" clas S: Which class I am with is a many-to-many relationship column: foreign key. I quote a foreign key column name than a person -         <!--CASCADE Cascade Operations: Save-update: Cascade Save Update Delete: Cascade Delete all: Cascade Save update + level Union Delete Conclusion: Cascade simplifies code writing. This property makes no use of the matter.                  It is recommended to use only save-update. If using the delete operation is too dangerous. Especially in many-to-many. Not recommended. -        <Setname= "Roles"Table= "Sys_user_role"Cascade= "Save-update" >            <Keycolumn= "user_id" ></Key>            <Many-to-manyclass= "Role"column= "role_id" ></Many-to-many>        </Set>

2. Operation

Action Association Properties

        // 3> User Expression Relationships         U1.getroles (). Add (R1);        U1.getroles (). Add (R2);                U2.getroles (). Add (R1);        U2.getroles (). Add (R2);                 // 4> Role Expression Relationships         r1.getusers (). Add (U1);        R1.getusers (). Add (U2);                R2.getusers (). Add (U1);        R2.getusers (). Add (U2);                 // 5> Call the Save method once save         Session.save (U1);        Session.save (U2);        Session.save (R1);        Session.save (R2);

3. Operation Advanced

Inverse property

    <!--Use the Inverse property true: Discard the maintain foreign key relationship false (default): Maintain relationship Conclusion: in the future, if you encounter many-to-many relationships in development. Be sure to choose one side to abandon maintenance off General who will give up to see the business direction.             For example, when entering an employee, you need to assign a role to the employee. Then the business direction is the employee maintenance role. Roles do not require maintenance and employee relationships. Role Abandonment Maintenance -                <Setname= "Users"Table= "Sys_user_role"Inverse= "true" >            <Keycolumn= "role_id" ></Key>            <Many-to-manyclass= "User"column= "user_id" ></Many-to-many>        </Set>

Cascading properties

　　

         <!--CASCADE Cascade Operations: Save-update: Cascade Save Update Delete: Cascade Delete all: Cascade Save update + level Union Delete Conclusion: Cascade simplifies code writing. This property makes no use of the matter.                  It is recommended to use only save-update. If using the delete operation is too dangerous. Especially in many-to-many. Not recommended. -        <Setname= "Roles"Table= "Sys_user_role"Cascade= "Save-update" >            <Keycolumn= "user_id" ></Key>            <Many-to-manyclass= "Role"column= "role_id" ></Many-to-many>        </Set>

Iii. Exercises: Adding contacts

Servlet:

    protected voidDoget (HttpServletRequest request, httpservletresponse response)throwsservletexception, IOException {//1> Gets the parameters and encapsulates the Linkman objectLinkman LM =NewLinkman (); Try{beanutils.populate (LM, Request.getparametermap ()); } Catch(illegalaccessexception e) {e.printstacktrace (); } Catch(InvocationTargetException e) {e.printstacktrace (); }        //2> Call service to save Linkman objectLMS. Save (LM); //3> Redirect to Linkman list (404)Response.sendredirect (Request.getcontextpath () + "/listlinkmanservlet"); }

Service

    PrivateCustomerdao CD =NewCustomerdaoimpl (); PrivateLinkmandao LMD =NewLinkmandaoimpl ();  Public voidSave (Linkman lm) {//Open Transactionhibernateutils.getcurrentsession (). BeginTransaction (); Try {            //1 obtaining Customer objects based on customer IDLong cust_id =lm.getcust_id (); Customer C=Cd.getbyid (cust_id); //2 Put the customer into Linkman to express the relationshipLm.setcustomer (c); //3 Save LinkmanLmd.save (LM); } Catch(Exception e) {e.printstacktrace (); //rolling back a transactionhibernateutils.getcurrentsession (). Gettransaction (). rollback (); }        //Commit a transactionhibernateutils.getcurrentsession (). Gettransaction (). commit (); }

Dao

     Public void Save (Linkman lm) {        ///1 GetSession Session Session        =  Hibernateutils.getcurrentsession ();        Session.save (LM);    }

Java EE Learning Note hibernate03: Multi-table operations, cascading exercises: adding contacts