Automatic filling of database public fields

introduction

Database tables of many projects will be set create_time、update_time Other public fields , These public fields need to be set when the database is created or updated ; If you set it yourself, you need to write extra set Code , Once there are many such watches, it will be troublesome ; So we can find a way to make these fields automatically filled ; and mybatis-plus It just provides such a function ;

mysql You can set the default value of the field CURRENT_TIMESTAMP Add the current time every time you insert data , Update can be set on update CURRENT_TIMESTAMP Implement the update operation to update the time ：

But I don't particularly recommend this method , If you let the database complete these logical operations, the responsibility is not clear , And it is not conducive to others to understand from the code ;

Here's how to use mybatis-plus Realize the automatic filling of public fields

Code operation

First you need to create a population data processor , Realization MetaObjectHandler：

/** * mybatis-plus Automatic attribute filling function provided  */
@Slf4j
@Component
public class MyMetaObjectHandler implements MetaObjectHandler {
    
    //  Insert data auto fill 
    @Override
    public void insertFill(MetaObject metaObject) {
    
        log.info(" New data is automatically filled ...");
        this.strictInsertFill(metaObject, "updateTime", Date.class, new Date());
        this.strictInsertFill(metaObject, "createTime", Date.class, new Date());
    }

    //  Update data auto fill 
    @Override
    public void updateFill(MetaObject metaObject) {
    
        log.info(" Update data auto fill ...");
        this.strictUpdateFill(metaObject, "updateTime", Date.class, new Date());
    }
}

The processor needs to be handed over to Sping management , add @Component annotation ;

Sometimes there will be createUser What fields , Add flexibly ：

After this step is completed , Next, just add @TableField annotation ：

@TableField(value = "create_time", fill = FieldFill.INSERT)
private Date createTime;

@TableField(value = "update_time", fill = FieldFill.INSERT_UPDATE)
private Date updateTime;

Mainly @TableField Annotated fill attribute ：

• INSERT Fill in when inserting
• UPDATE Fill in on update
• INSERT_UPDATE Both update and insert are populated
• DEFAULT By default , Nothing is filled
  

In this way, the automatic filling is set , You can test ：

The new data

Update data

In the database create_time and update_time They also have corresponding values ：

In this way, the overall automatic filling operation, that is, configuration, is completed ;

Step on the pit diary ： Automatic filling principle

There is a problem in writing this project ： update operation update Auto fill does not take effect when ;

After investigation, it is found that the updated data comes from the front end update_time Field Already exist A time value （ I found this value from the database ）;

So I guess If the field to be automatically filled already has a value , Then the automatic filling mechanism will no longer fill the field with values ;

---

Because auto fill takes effect and strictUpdateFill() Methods matter （ Take update as an example ）, So I debug Check its source code ：

First of all, no matter whether there is a value in the automatic filling, it will enter the method ：

Then enter the method ：

Then through a round-trip call （ You can try it yourself , Don't show if it's not important ）, Came to the following method ：

This method can show the strategy of automatic filling ： Only when the public fill field is empty, it will be automatically filled ; Briefly explain the key code ：

• fieldName: Public fill field name
• fieldVal: Generated public fill field values

if (metaObject.getValue(fieldName) == null) {
     //  Judge whether the value of the public fill field is empty , If it is empty, it will be filled automatically , Not empty, end directly 
	Object obj = fieldVal.get(); //  Get the automatically generated fill value 
	if (Objects.nonNull(obj)) {
     //  Judge whether the filling value is empty 
	metaObject.setValue(fieldName, obj); //  Assign the filling value to this field , Realize the automatic filling of public fields 
	}
}

Of course, there are still some steps to follow , Here is just a list of the key steps ;

---

Then I put update_time The field is manually assigned a null value before being passed to the backend , Auto fill takes effect ;

summary

in general , Automatic filling of public fields is still very easy to use , Save a lot of code ; Of course, one thing to keep in mind ： Make sure that the fields that need to be automatically filled are empty , Only in this way can the automatic filling mechanism take effect

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