为什么在gorm之类的go库中的struct中使用sql标记？

Question

Well I know the necessity of tags in struct in golang and how is it accessed by reflect in golang. But I have searched and could not find a reliable answer to the question of why I should use sql tags in struct while writing struct for sql results. I have explored many sample code and people are using sql:"index" in the struct and sql:"primary_key" in the struct.

Now I have done indexing in the database layer, isn’t it enough? Should I have to use sql:"index" too get the best results? Like so I have defined primary key attribute in the database should I have to specify sql:"primary_key" as well?

My code seems to work fine without those. Just want to know their benefit and usages.

Answer 1

I think you are referring to an ORM library like gorm

In that case, metadata like sql:"primary_key" or sql:"index" will just tell the ORM to create an index while trying to setup the tables or maybe migrate them.

A couple of examples in gorm could be: indexes, primary keys, foreign keys, many2many relations or when trying to adapt an exiting schema into your gorm models, setting the type explicitly, like for example:

type Address struct {
    ID       int
    Address1 string         `sql:"not null;unique"` // Set field as not nullable and unique
    Address2 string         `sql:"type:varchar(100);unique"`
    Post     sql.NullString `sql:"not null"`
}