Introduction

What are computed properties? Computed properties are not simple wrapper types or basic types, but properties derived through conversion functions or calculations.

Computed properties can be divided into two major categories: in-memory computed properties and database computed properties

Differences

Computed Property	vo	Difference
In-memory computed property	If entity has @Column, then vo or dto must also have corresponding conversion	Function acts on the retrieved value, function will be applied to the value at the Java layer
Database computed property	vo or dto only needs property name consistency or manual as	Function acts at the database layer, retrieved value is already converted

In-memory Computed Properties

• json property private UserExtra userExtra; used to describe database stored string or json type, mapped to java object, supports filtering, return sorting, etc.
• collection property private List<UserLabels> userLabels; used to describe database stored string or json type, mapped to java collection, supports filtering, return sorting, etc.
• Enum property private UserStatusEnum userStatus; used to describe database stored string or number type, mapped to java enum property, supports filtering, return sorting, etc.

Database Computed Properties

• Enhanced property private String idCard; automatically adds base64 encoding when writing to database and automatically decodes when reading, supports filtering, return sorting, etc.
• Simple computed property: composite property private String fullName; it is composed of firstName and lastName, or age, which is a dynamic value generated by subtracting the current time and birthday, supports filtering, return sorting, etc.
• Status computed property: for example, you have a certificate table, the certificate table has certificate expiration time, then the certificate has a dynamic hidden property called status, whether the certificate has expired can be implemented through this status
• Complex computed property: composed of sub-table or additional table data, such as private Integer StudentSize; if class and user are one-to-many, then this property is used to describe how many students are in the class, supports filtering sorting return
• Function auto-increment property: this property can have data generated by the database, such as the database function has mysqlNextId() or gis generated by the database function, then it is applicable to this method only effective when inserting

The difference between in-memory computed properties and database computed properties is