In fact, Dao generally does not have this class, which generally refers to the concept of model in the MVC architecture in java, mainly some methods of accessing the database.
The outermost layer in the general javaMVC architecture is the view, which is the page, the control is some classes that control the background and page access, the model is actually the dao layer, but most people will add another layer of service layer to provide more convenient applications
PO (persistant object) Persistent object
is the concept of o/r mapping. If there is no o/r mapping, this concept will not exist. Usually it corresponds to the data model (database), and it also has some business logic processing. Yes It is regarded as a java object mapped to a table in the database. The simplest PO is a record in a table in the database, and multiple records can use a collection of POs. PO should not contain any operations on the database.
VO (value object) The value object
is usually used for data transfer between business layers. Like PO, it only contains data. But it should be an abstract business object, which can correspond to a table or not, depending on the needs of the business . Personally feel that it is the same as DTO (data transfer object), which is passed on the web.
BO (business object)
From the perspective of the business model, see the domain object in the UML component domain model. The java object that encapsulates the business logic, by calling the DAO method, combined with PO and VO to perform business operations.
POJO(plain ordinary java object) Simple and irregular java object is
a pure traditional java object. That is to say, in some Object/Relation Mapping tools, the persistent object that can maintain database table records is completely a pure Java Bean specification. Java object, no other properties and methods are added. My understanding is the most basic Java Bean, only property fields and setter and getter methods! .
DAO (data access object) The data access object
is a standard j2ee design pattern of sun. One interface in this pattern is DAO, which is responsible for the operation of the persistence layer. It provides an interface for the business layer. This object is used to access the database. Combined use, DAO contains various database operation methods. Through its methods, combined with PO to perform related operations on the database. It is sandwiched between business logic and database resources. With VO, it provides database CRUD operations...
DTO (Data Transfer Object) data transfer objects
are mainly used for remote calls and other places that require a large number of transfer objects.
For example, if our table has 100 fields, then the corresponding PO has 100 attributes.
However, we only need to display 10 fields on the interface, and the
client uses WEB service to obtain data. There is no need to pass the entire PO object to the client.
At this time, we can use the DTO with only these 10 attributes to pass the result to the client. This will not expose the server-side table structure. After reaching the client, if this object is used to display the corresponding interface, then its identity will be changed to VO
O/R Mapper Object/Relational Mapping
After all mappings are defined, this O/R Mapper can help us do a lot of work. Through these mappings, this O/R Mapper can generate all the information about object save, delete, and read SQL statement, we no longer need to write so many lines of DAL code.
Entity Model (Entity Mode)
DAL (Data Access Layer)
IDAL (Interface Layer)
DALFactory (Class Factory)
BLL (Business Logic Layer)
BOF Business Object Framework Business Object FrameworkSOA
Service Orient Architecture Service Oriented
DesignEMF Eclipse Model Framework Eclipse Modeling Framework
Five Objects of Java
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VO:value object value object
It is usually used for data transfer between business layers. Like PO, it only contains data. But it should be an abstracted business object, which can correspond to a table or not, depending on the needs of the business. Personally, I feel that it is the same as DTO (Data Transfer Object), which is passed on the web.
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DAO: data access object data access object
This object is used to access the database. Usually used in conjunction with PO, DAO contains the working methods of various databases. Through its method, the relevant * operation is performed on the database in combination with PO.
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POJO: plain ordinary java object
I personally feel that it is not on the same level as other things, and both VO and PO should belong to it.
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PO:persistant object Persistent object
It can be seen as a java object mapped to a table in the database. The simplest PO corresponds to a record in a table in the database, and multiple records can use a collection of POs. The PO should not contain any *operations on the database.
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BO:business object business object
The java object that encapsulates the business logic, by calling the DAO method, combined with PO and VO to perform business operations.
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