Often exposed toVO，DO，DTOThis paper briefly analyzes these concepts from the perspectives of entity division in field modeling and actual application in projects.
The main conclusions drawn are: in project applications,VOCorresponding to the data (form) that needs to be displayed on the page,DOCorresponding to the data stored in the database (data table),DTOCorresponding to data that needs to be passed in addition to both.
1. Entity Class
The definition of entity classes in Baidu Encyclopedia is as follows:
The main responsibility of an entity class is to store and manage information inside the system. It can also have behaviors, even complex behaviors, but these behaviors must be closely related to the entity objects it represents.
Based on the above definition, we can understand that entity classes have two aspects: storing data and executing operations related to the data itself. The simplest entity class isPOJOClass, containing attributes and attributes corresponding tosetandgetMethods, common methods of entity classes are also used to output their own data.toStringmethod.
2. Entity classes in domain models
The entity classes in the domain model are divided into four types:VO、DTO、DO、PO, Various entity classes are used for interactions between different business levels, and will realize transformation between entity classes within the level.
Business hierarchy is: View layer (VIEW+ACTION), service layer (SERVICE), persistent layer (DAO）
The transmission of the corresponding entities between the layers is as follows:
We do not strictly follow this transmission relationship in the project, but this correlation with the business level is helpful for us to understand the role of various entity classes. (We have not been exposed toPOI understand the reasonORMrightPOEncapsulated)
The following is the original text of the data, and the above picture is drawn based on this:
concept:
VO（View Object）：A view object, used for display layer, is used to encapsulate all data from a specified page (or component).
DTO（Data Transfer Object）：The concept of data transmission object comes fromJ2EEThe original design pattern was toEJBThe distributed application provides coarse-grained data entities to reduce the number of distributed calls, thereby improving the performance of distributed calls and reducing network load, but here, I generally refer to data transmission objects used between the display layer and the service layer.
DO（Domain Object）：Domain objects are tangible or intangible business entities abstracted from the real world.
PO（Persistent Object）：Persistent object, which forms a one-to-one mapping relationship with the data structure of the persistent layer (usually a relational database). If the persistent layer is a relational database, then each field (or several) in the data table corresponds to it.POone (or several) properties of .
Model:
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III. Entity classes in the project
Common entity classes in projects includeVO，DOandDTO, naming rules are often ending with corresponding strings, such as*. butDTOThis rule is not always followed, but is usually related to its purpose, such as*, means that a query condition is stored. The business level of entity classes in the project is not so strict. For example, we can assemble one in the view layer.DO, you can also add oneVOThe division method associated with business hierarchy appears to be somewhat redundant. The abstract understanding from the project code is:VOCorresponding to the data to be displayed on the page,DOCorresponding to the data stored in the database,DTOCorresponding to data that needs to be passed in addition to both.
PO(persistant object) persistent object
The concept that appears during o/r mapping, if there is no o/r mapping, no this concept exists. Usually, it corresponds to the data model (database), and it also has some business logic processing. It can be regarded as a java object that maps to the tables in the database. The simplest PO is a record in a table in the database, and multiple records can be set of POs. The PO should not contain any operations on the database.
DO (Domain Object) Domain Object
It is a tangible or intangible business entity abstracted from the real world.
TO(Transfer Object) , data transmission object
Objects transferred between different tie(relationship) of the application
DTO (Data Transfer Object) Data Transfer Object
This concept comes from the J2EE design pattern. The original purpose was to provide coarse-grained data entities for distributed applications of EJB to reduce the number of distributed calls, thereby improving the performance of distributed calls and reducing network load. However, here, I generally refer to data transmission objects used between the display layer and the service layer.
VO(value object) value object
It is usually used for data transfer between business layers, and just like POs, it only contains data. But it should be abstracted business objects, which can correspond to tables or not, depending on the needs of the business. Created with the new keyword, recycled by GC.
BO(business object) business object
From the perspective of business model, see the domain objects in the UML component domain model. A java object that encapsulates business logic, performs business operations by calling the DAO method, combined with PO and VO. business object: The main function of the business object is to encapsulate the business logic into an object. This object may include one or more other objects. For example, a resume has educational experience, work experience, social relations, etc. We can correspond to educational experience with a PO, work experience with a PO, and social relations with a PO. Create a BO object corresponding to the resume to process resumes, each BO contains these POs. In this way, when we process business logic, we can process it against BO.
POJO(plain ordinary java object) Simple and non-rules java object
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 object that complies with the Java Bean specifications, without adding other attributes and methods. My understanding is the most basic Java Bean, with only attribute fields, setter and getter methods! .
DAO(data access object) Data access object
It is a standard j2ee design pattern of sun. There is an interface in this pattern that is DAO, which has negative persistence layer operations. Provides interfaces for the service layer. This object is used to access the database. Usually used in combination with PO, DAO includes various database operation methods. Through its method, it combines PO to perform related operations on the database. Clipped between business logic and database resources. In conjunction with VO, provide CRUD operations of the database.