Postgres UUID Types. about xo HOT 7 CLOSED

UUID is a custom PostgreSQL type. You need to supply a package that supports that type via either the --custom-type-package or -C. That type needs to be Marshal'able by the PostgreSQL Go driver to the database. That's fairly easy to do -- you only need to supply compatible Scanner and Valuer interfaces for that UUID type. You can see an example of that in the generated xo_db.xo.go file, which provides a StringSlice type for working with string arrays in PostgreSQL.

This is an artifact of working with static typing in both PostgreSQL and Go. If you don't want to create a type that supports the Scanner or Valuer interface, then you might want to consider storing your UUIDs as strings (text/varchar/etc) in the database instead, and creating a UUID index over that field, as well as a CHECK() constraint.

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Oh -- one quick note -- if you want to just quickly generate your schema and later come back to write the Go types for your custom database types, then you can use -C pgtypes, which contains all the PostgreSQL custom defined types and is in the xo/examples/pgtypes directory.

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Got it! Thx.

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Hi! I'm having the same issue, @whitebook. Do you have an example of how you got this to work?

ps -- thanks for this great package, @kenshaw

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PostgreSQL's UUID isn't supported in full by the lib/pq driver -- it just sends the read/writes the UUID as a string. All you need to do is define a UUID type supporting the Scanner and Valuer interfaces. You can put this in the same output directory as xo writes to, or you can use some other package that has predefined types and the name of that package via the --custom-type-package command line option.

I'm fairly certain all you need to do is define a type alias in Go like this:

// go/src/github.com/knq/mycustomtypes/mycustomtypes.go
package mycustomtypes

type UUID string

You would just need to then do this:

xo --custom-type-package mycustomtypes -o models pgsql://user:pass@host/dbname

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Thanks, @kenshaw. I'll give that a try.

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Thanks again for your help, @kenshaw. Just to close the loop in case others have this question, this is what I did:

First, I created a file called "uuid.go" in the same directory as the generated xo models. It's content is:

package models

import (
    "database/sql/driver"
    "errors"
)

// UUID defines the postgres UUID custom type
type UUID struct {
    Val string
}

// Scan satisfies the sql.Scanner interface for UUID.
func (ss *UUID) Scan(src interface{}) error {

    buf, ok := src.([]byte)
    if !ok {
        return errors.New("invalid UUID")
    }

    *ss = UUID{string(buf)}
    return nil

}

// Value satisfies the driver.Valuer interface for UUID.
func (ss UUID) Value() (driver.Value, error) {
    return ss.Val, nil
}

I could then call it using this:

    project, err := models.ProjectByID(db, models.UUID{"d0bf9d77-cd81-4ad6-ace0-f0be928574a2"})

Might not be exactly right, but it seems to be working for me so far.

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