如何将文本列的值指定为字符串并集？

Question

我有一个结构：Document

type Document struct {

    ID               entity.EntityID

    Type             string

    ContentType      files.MIMEType

    URL              string

    UploadedByUserID entity.EntityID

    CreatedAt        time.Time

}

type MIMEType string

const (

    MIMETypeJPG MIMEType = "image/jpeg"

    MIMETypePDF MIMEType = "application/pdf"

    MIMETypePNG MIMEType = "image/png"

    MIMETypeTXT MIMEType = "text/plain"

)

它映射到一个表，其中列的类型为：documentsContentTypevarchar(1024)

create table documents(

    id bigint not null default nextval('documents_id_seq') PRIMARY KEY,

    url varchar(1024) not null,

    type varchar(1024) not null,

    content_type varchar(1024) not null,

    uploaded_by_user_id bigint,

    created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP not null

);

Create(&d)其中 是一个实例给我一个错误：dDocument

[2.530ms] [rows:1] INSERT INTO "documents" ("type","content_type","url","uploaded_by_user_id","created_at") VALUES ('other_freight','image/png','https://lateralline-documents-dev.s3.us-west-2.amazonaws.com/doc-other_freight-2021_08_25__11_15_13_379569000.png','253608954016301056','2021-08-25 11:15:13.82') RETURNING "id"

interface conversion: interface {} is files.MIMEType, not string

我想告诉gorm，当我读取和写入字段时，它不仅仅是一个任意字符串，它应该是一个值。有没有办法做到这一点？我在其他 ORM 中也看到了此功能。documents.content_typefiles.MIMEType

Answer 1

您可能需要查看 中的自定义类型（或检查此答案）。go-gorm简而言之，您需要为结构实现 和 接口。ScannerValuerMIMETypefunc (m *MIMEType) Scan(value interface{}) error {  val, ok := value.(string)  if !ok {    return errors.New(fmt.Sprint("Failed to unmarshal string value:", value))  }    *m = MIMEType(val)  return nil}func (m MIMEType) Value() (driver.Value, error) {  return string(m), nil}