There are multiple ways that a graphQL type can be bound to a Go struct that allows for many usecases.
Bind directly to struct field names
This is the most common use case where the names of the fields on the Go struct match the names of the fields in the graphQL type. If a Go struct field is unexported, it will not be bound to the graphQL type.
type Car struct {
Make string
Model string
Color string
OdometerReading int
}
And then in your graphQL schema:
type Car {
make: String!
model: String!
color: String!
odometerReading: Int!
}
And in the gqlgen config file:
models:
Car:
model: github.com/my/app/models.Car
In this case, each field in the graphQL type will be bound to the respective field on the go struct ignoring the case of the fields
Bind to a method name
This is also very common use case that comes up where we want to bind a graphQL field to a Go struct method
type Person struct {
Name string
}
type Car struct {
Make string
Model string
Color string
OwnerID *string
OdometerReading int
}
func (c *Car) Owner() (*Person) {
// get the car owner
//....
return owner
}
And then in your graphQL schema:
type Car {
make: String!
model: String!
color: String!
odometerReading: Int!
owner: Person
}
And in the gqlgen config file:
models:
Car:
model: github.com/my/app/models.Car
Person:
model: github.com/my/app/models.Person
Here, we see that there is a method on car with the name Owner
, thus the Owner
function will be called if
a graphQL request includes that field to be resolved.
Model methods can optionally take a context as their first argument. If a context is required, the model method will also be run in parallel.
Bind when the field names do not match
There are two ways you can bind to fields when the the Go struct and the graphQL type do not match.
The first way is you can bind resolvers to a struct based off of struct tags like the following:
type Car struct {
Make string
ShortState string
LongState string `gqlgen:"state"`
Model string
Color string
OdometerReading int
}
And then in your graphQL schema:
type Car {
make: String!
model: String!
state: String!
color: String!
odometerReading: Int!
}
And in the gqlgen config file add the line:
struct_tag: gqlgen
models:
Car:
model: github.com/my/app/models.Car
Here even though the graphQL type and Go struct have different field names, there is a Go struct tag field on longState
that matches and thus state
will be bound to LongState
.
The second way you can bind fields is by adding a line into the config file such as:
type Car struct {
Make string
ShortState string
LongState string
Model string
Color string
OdometerReading int
}
And then in your graphQL schema:
type Car {
make: String!
model: String!
state: String!
color: String!
odometerReading: Int!
}
And in the gqlgen config file add the line:
models:
Car:
model: github.com/my/app/models.Car
fields:
state:
fieldName: LongState
Binding to Anonymous or Embedded Structs
All of the rules from above apply to a struct that has an embedded struct. Here is an example
type Truck struct {
Car
Is4x4 bool
}
type Car struct {
Make string
ShortState string
LongState string
Model string
Color string
OdometerReading int
}
And then in your graphQL schema:
type Truck {
make: String!
model: String!
state: String!
color: String!
odometerReading: Int!
is4x4: Bool!
}
Here all the fields from the Go struct Car will still be bound to the respective fields in the graphQL schema that match
Embedded structs are a good way to create thin wrappers around data access types an example would be:
type Cat struct {
db.Cat
//...
}
func (c *Cat) ID() string {
// return a custom id based on the db shard and the cat's id
return fmt.Sprintf("%d:%d", c.Shard, c.Id)
}
Which would correlate with a gqlgen config file of:
models:
Cat:
model: github.com/my/app/models.Cat
Binding Priority
If a struct_tags
config exists, then struct tag binding has the highest priority over all other types of binding.
In all other cases, the first Go struct field found that matches the graphQL type field will be the field that is bound.