Support for multiple/composite primary keys on new relation tag `pg:"rel:"`

[vilipwong]

As previously discussed in Discord, there are problems in query generation when using multiple primary keys

A quick fix has been done in 5882d9f to address the issue i raised. However it occur for other relations as well, rel:has-one,has-many etc, more details below:

Expected Behavior

I should be able to retrieve ProjectDocument with Project relation with relation tag has-one, has-many,belongs-to

Current Behavior

encounter panic: pg: ProjectDocument has-one Project: ProjectDocument must have column project_company_id (use fk:custom_column tag on Project field to specify custom column)

Steps to Reproduce

CREATE TABLE projects
(
  id              VARCHAR(128) ,
  company_id              VARCHAR(128) ,
  PRIMARY KEY (company_id, id)
);
CREATE TABLE documents
(
    id                           VARCHAR(128) ,
    company_id              VARCHAR(128) ,
    PRIMARY KEY (company_id, id)
);
CREATE TABLE project_documents
(
    company_id              VARCHAR(128) ,
    project_id              VARCHAR(128) ,
    document_id              VARCHAR(128) ,
    PRIMARY KEY(company_id, project_id, document_id),
    FOREIGN KEY (company_id, project_id) REFERENCES projects (company_id, id),
    FOREIGN KEY (company_id, document_id) REFERENCES documents (company_id, id)
);

package main

import (
    "fmt"

    "github.com/caarlos0/env"
    pg "github.com/go-pg/pg/v10"
    "github.com/go-pg/pg/v10/orm"
)

// DB Configuration
type DB struct {
    Address      string `env:"DB_ADDRESS,required"`
    Port         string `env:"DB_PORT,required"`
    Username     string `env:"DB_USERNAME,required"`
    Password     string `env:"DB_PASSWORD,required"`
    DatabaseName string `env:"DB_NAME,required"`

    EnableLogging bool `env:"DB_ENABLE_LOGGING"`
}

// New up DB config
func New() (*DB, error) {
    d := &DB{}
    err := env.Parse(d)
    return d, err
}

// Connect to DB
func (d *DB) Connect() (*pg.DB, error) {
    opts := &pg.Options{
        User:     d.Username,
        Password: d.Password,
        Database: d.DatabaseName,
        Addr:     d.Address + ":" + d.Port,
    }
    db := pg.Connect(opts)

    _, err := db.Exec("SELECT")
    return db, err
}

func main() {
    qwe := &ProjectDocument{
        ID:        "bsvt22v0cr8rnl249230",
        CompanyID: "a9543f45-5ea3-4bcb-81c6-1cba6c278f6d",
    }

    c, _ := New()
    db, _ := c.Connect()

    err := db.Model(qwe).
        WherePK().
        Relation("Project").
        Select()

    fmt.Println("@@@ res", err)

}

type Project struct {
    ID        string     `json:"id" pg:",pk"`
    CompanyID string     `json:"companyID" pg:",pk"`
    Documents []Document `pg:",many2many:project_documents" json:"documents,omitempty"`
}

type Document struct {
    ID        string `json:"id" pg:",pk"`
    CompanyID string `json:"companyID" pg:",pk"`
    Name      string `json:"name"`
}

type ProjectDocument struct {
    CompanyID  string    `json:"companyID" pg:",pk"`
    ProjectID  string    `json:"projectID" pg:",pk"`
    Project    *Project  `json:"project" pg:"rel:has-one"`
    DocumentID string    `json:"documentID" pg:",pk"`
    Document   *Document `json:"document"`
}

func init() {
    orm.RegisterTable((*ProjectDocument)(nil))
}

Context (Environment)

I am trying to link projects into project documents with a tenant key company_id using citus, thus all of the tables have multiple primary keys

Detailed Description

Possible Implementation

[vmihailenco]

Please try v10.4.0