Retrieving many-to-many results from GORM - mysql

Question

I am mapping my database using gorm.
I have two tables (service and resource) with a many-to-many relationship. I am modelling them in code as such:
type Service struct {
BaseModel
Name string `gorm:"not null;unique_index"`
Resources []Resource `gorm:"many2many:service_resource"`
}
type Resource struct {
BaseModel
Name string `gorm:"not null;unique_index"`
}
Using gorm's AutoMigrate the following tables are created:
(I also executed a raw SQL query to add the id primary key in the mapping table.)
To create a new service, I use the following code:
service := Service{
Name: "core",
Resources: []Resource{
{Name: "ec2"},
{Name: "dynamo"},
},
}
db.Create(&service)
This creates all the resources along with the service and fills in the relationship between them in the service_resource table just fine, as expected.
However, my problem is when I'm querying for the services. I use the following code to retrieve all services:
services := []model.Service{}
db.Find(&services)
This returns successfully with the services array populated, but the Resources array of each service is empty:
"services": [
{
"ID": 1,
"Name": "core",
"Resources": null
},
...
]
I was under the assumption that gorm would populate it automatically. Is there some step that I'm missing?

Answer 1

You need to Preload the resources field before querying for services:
services := []model.Service{}
db.Preload("Resources").Find(&services) // error checking ommited
This correctly populates the Resources field of every service.