Load,get; Find,iterator; The difference between merge,saveorupdate,lock

First, Load,get
(1) When the record does not exist, the Get method returns the Null,load method to produce an exception

(2) The Load method can return the entity's proxy class, and the Get method returns the real entity class

(3) The Load method can take full advantage of Hibernate's internal cache and the existing data in the level two cache, while the Get method only makes data lookups in the internal cache, and if no data is found it will go over the level two cache and call the SQL query database directly.
    (4)   Perhaps others have modified the data in the database, how load finds the data in the cache, no longer accesses the database, and get returns the most recent data.
 
Second, Find,iterator
      (1) Iterator first gets the ID of the qualifying record, and then finds the data in the local cache with the ID. Found in the database again, the result is in the cache again. N+1 SQL.
(2) Find generates SQL statements directly to the database, the data found in the cache, a SQL.

Three, hibernate-generated DAO class function function description (merge,saveorupdate,lock)

/**
* Copy the properties of the object that passed in the detached state to the persisted object and return the persisted object.
* If there are no persisted objects associated with the session, load one.
* If the incoming object is not saved, a copy is saved and returned as a persistent object, and the incoming object remains in the detached state.
*/
Public sysuser Merge (Sysuser detachedinstance) {
Log.debug ("Merging Sysuser instance");
try {
Sysuser result = (Sysuser) gethibernatetemplate (). Merge (
Detachedinstance);
Log.debug ("merge successful");
return result;
} catch (RuntimeException re) {
Log.error ("Merge Failed", re);
throw re;
}
}

/**
* Persist the incoming object and save it. If the object is not saved (transient state), the Save method is called.
* If the object is saved (detached state), call the Update method to re-associate the object with the session.
*/
public void Attachdirty (Sysuser instance) {
Log.debug ("Attaching dirty Sysuser instance");
try {
Gethibernatetemplate (). Saveorupdate (instance);
Log.debug ("Attach successful");
} catch (RuntimeException re) {
Log.error ("Attach failed", re);
throw re;
}
}

/**
* Set the incoming object state to the transient state
*/
public void Attachclean (Sysuser instance) {
Log.debug ("Attaching clean Sysuser instance");
try {
Gethibernatetemplate (). Lock (instance, lockmode.none);
Log.debug ("Attach successful");
} catch (RuntimeException re) {
Log.error ("Attach failed", re);
throw re;
}
}

Load,get; Find,iterator; The difference between merge,saveorupdate,lock