Day 6 of Hibernate

1. Place the entire inheritance relationship in a table. To distinguish specific subclass information, an additional column needs to be created in the table.
Create Table paymeny (
.....
Type varchar2 (12)
);
<Class name = "Payment" table = "Payment">
.....
<Discriminitor column = "type" type = "string">
<Sub-class name = "cardpayment" discriminitor-value = "card">
Subclass attributes
</Sub-class>
<Sub-class name = "cashpayment" discriminitor-value = "cash">
Subclass attributes
</Sub-class>
</Class>
High Efficiency and Polymorphism
Redundant waste of space
2. Combine the parent class information with each subclass information to create multiple specific tables.
Create Table cardpayment (
Parent class information
Credit card subclass Information
)
Create Table cashpayment (
Parent class information
Cash subclass Information
)
<Class name = "Payment">
.....

<Union-sub-class name = "cardpayment" table = "cardpayment">
Subclass attributes
</Union-sub-class>
<Union-sub-class name = "cashpayment" table = "cashpayment">
Subclass attributes
</Union-sub-class>
</Class>
Convenient operations, high efficiency, high space utilization
No polymorphism in redundancy
3. Create the corresponding table for each specific object
Create Table payment (
Parent class information
)
Create Table cardpayment (
Credit card subclass Information
Foreign key cardid
)
Create Table cashpayment (
Cash subclass Information
Foreign key cashid
)
<Class name = "Payment" table = "Payment">
.....

<Joined-sub-class name = "cardpayment" table = "cardpayment">
<Key column = "cardid"> </key>
Subclass attributes
</Joined-sub-class>
<Joined-sub-class name = "cashpayment" table = "cashpayment">
<Key column = "cashid"> </key>
Subclass attributes
</Joined-sub-class>
</Class>
High utilization of polymorphism without redundant Space
Inefficient operations

Hibernate query:
1 native SQL
Programmers are proficient in SQL
Control SQL efficiency by yourself
The queried information can only be encapsulated by yourself.
2 hql student1 ---- 1 Address
Based on the SQL framework, object-oriented
From student;
Select S. name from student s;
From student s where S. age> 20;
From student s inner join address a where a. Name = ...;
3 criteria
Standard Object-Oriented Query
Session. createcriteria (student. Class );
Session. createcriteria (student. Class)
. Add (restrictions. gt ("Age", 20 ));
Session. createcriteria (student. Class)
. Createcriteria ("Address ")
. Add (restrictions. eq ("name ","..."));
4 named Query
Extract SQL statements from source code to the ing File
*. HBM. xml
<Hibernate-mapping>
<Class>
.....
</Class>
<Query name = "SQL variable name">
<! [CDATA [
Hql statement ...? /: Name
]>
</Query>
</Hibernate-mapping>

Session. getnamedquery ("SQL variable name ")

Hibernate supports data sources:
1 hiebrnate built-in data source, used for testing only
<Property name = "connection. username"> Scott </property>
<Property name = "connection. url">
JDBC: oracle: thin: @ localhost: 1521: sinojava
</Property>
<Property name = "dialect">
Org. hibernate. dialect. oracle9dialect
</Property>
<Property name = "connection. Password"> tiger </property>
<Property name = "connection. driver_class">
Oracle. JDBC. Driver. oracledriver
</Property>

2 ******* integrate c3p0 with hibernate *******
<Property name = "connection. username"> Scott </property>
<Property name = "connection. url">
JDBC: oracle: thin: @ localhost: 1521: sinojava
</Property>
<Property name = "dialect">
Org. hibernate. dialect. oracle9dialect
</Property>
<Property name = "connection. Password"> tiger </property>
<Property name = "connection. driver_class">
Oracle. JDBC. Driver. oracledriver
</Property>

Add the following information:
<Property name = "connection. provider_class">
Org. hibernate. Connection. c3p0connectionprovider
</Property>
<Property name = "c3p0. max_size"> 5 </property>
<Property name = "c3p0. Timeout"> 2000 </property>
..........

3. JNDI
<Property name = "connection. username"> Scott </property>
<Property name = "connection. url">
JDBC: oracle: thin: @ localhost: 1521: sinojava
</Property>
<Property name = "dialect">
Org. hibernate. dialect. oracle9dialect
</Property>
<Property name = "connection. Password"> tiger </property>
<Property name = "connection. driver_class">
Oracle. JDBC. Driver. oracledriver
</Property>

Add the following information:
<Property name = "JNDI"> JAVA: COMP/ENV/userds </property>

The program must manually obtain the connection and pass it to hibernate:
Getsession (){
Context Env = new intialcontext ();
Datasource DS = (datasource) ENV. Lookup ("Java: COMP/ENV/userds ");
Conenction con = Ds. getconnection ();
...
Sessionfactory. opensession (conn );
....
}

Hibernate supports paging:
Query. setfirstresult (start position );
Query. setmaxresults (number of queries );
Query. List ();

Lock:
Read/write locks
Table-Level Lock/column-Level Lock

Concurrency Control in JDBC:
1 Database
Isolation level
Transaction_none 0
Transaction_uncommited_read 1
Transaction_commied_read 2
Transaction_repeatable_read 4
Transantion_serializable 8
Connection. settransactionisolation (...)

Select ***** [for update ];
2 applications
Synchronized
* ***** Hibernate controls multi-thread concurrency:
1 Database
Isolation level
Transaction_none 0
Transaction_uncommited_read 1
Transaction_commied_read 2
Transaction_repeatable_read 4
Transantion_serializable 8

Hibernate. cfg. xml
<Property name = "connection. Isolation"> 2 </property>

Select ***** [for update ];
2 applications
Pessimistic lock:
It is assumed that two threads will access one data simultaneously.
The operation must be locked:
Query q = session. createquery ("from student s ")
Q. setlockmode ("S", lokemode. Write );
Lockmode:
None
Read lock
Write lock
Update table-Level Lock <==> select *** for update;
Optimistic lock:
It is considered that a thread may not necessarily be concurrently accessed.

Thread 1 thread 2
------------------------------------------------------
Balance = 1000
1000 1000
1000-600 commit
400 1000-200 commit
800

Solution: Use a flag to Control Data Validity

Balance identity thread 1 thread 2
-----------------------------------------------------------------
1000 1
1000 1 1000 1
1000-600 1 + 1 commit
400 if (2> 1) Submit
1000-200 1 + 1 commit
If (2> 2) cannot be submitted

Flag space:
Timestamp:

** Version:

Hibernate cache mechanism:
Level 1 cache: Session Object
Session. Get (class, serializble)
Session. Load (class, serializble)

GET/load commonalities:
The SQL statement structure sent by get and load is the same.
Session ---> sessionfactory ---> DB
Difference between get and load:
Get:
1. If you call the get method, you can directly send an SQL query.
2. Get directly searches for information. If no information is found, null is returned.

Load:
1. The load method is called and no SQL statement is sent by default.
SQL query is not sent until this object is actually used.
Object returned by the load method: If no information is found, the proxy object is returned.
If the information is used, the actual object 2 load method cannot be found, and an exception org. hibernate. objectnotfoundexception is reported.

Level 2 Cache: sessionfactory
1. Add attributes to hibernate. cfg. xml.
-- Set the second-level cache class
<Property name = "cache. provider_class">
Org. hibernate. cache. ehcacheprovider
</Property> Level 2
-- Sets the cache for query operations. Otherwise, the cache takes effect for get/load.
<Property name = "cache. use_query_cache"> true </property>

2. Set the secondary cache in the HBM ing File
<Class name = "concur" table = "concur_time">
<Cache Usage = "Read-Only | read-write"/>
...
</Class>

3. If you use a query statement to query and want to use a second-level cache
Query. setcacheable (true );
Query. list ....

Hibernate object status and session methods:
Transient temporary object
Detached free object
Persist persistence object

Configuration CFG = new configuration (). Configure ();
Sessionfactory Sf = cfg. buildsessionfactory ();
Session session = SF. opensession ();
Transaction Tx = session. begintransaction (); Memory session DB

Concur c = new concur ("hehe"); there is no === transient
Bytes ----------------------------------------------------------------------------------------------
Session. Save (C );

TX. Commit (); has a === persist
Bytes ----------------------------------------------------------------------------------------------
Session. Close (); no === detched
Bytes ----------------------------------------------------------------------------------------------

1. Build a hibernate Environment
2. hibernate operation steps
3 1-1 1-m
4. inheritance relationship processing: 3 methods
5 optimistic lock
6. HBM configuration file
7. Common Methods of session
8 hql/criteria
9 Data Source-c3p0
10 Id generation policy-native (sequence, identity, HiLo)-UUID. HEX