In a nutshell, GraphQL is about asking for specific objects' attributes.
HAL objects are described here. Each object can be queried by GraphQL, so that using a simple query it is possible to fetch specific fields for each object. For example, if you want to get the name field for all triggers, the following request can be used:
query { allTriggers { name }}
{
"data": {
"allTriggers": [
{
"name": "My first trigger"
},
{
"name": "My second trigger"
},
{
"name": "My third trigger"
}
]
}
}
The query response can be further refined by supplying filter and orderBy arguments. For example, for the Trigger object, you can use this query to get a specific record:
query {
allTriggers(filter: {name: {eq: "My first trigger"}}) {
name
}
}
{
"data": {
"allTriggers": [
{
"name": "My first trigger"
}
]
}
}
Interfaces
Before you can start using GraphQL queries, you need to get familiar with the concept of interface.
Like many type systems, GraphQL supports interfaces. An Interface is an abstract type that includes a certain set of fields that a type must provide to implement the interface.
For example, in HAL every trigger must implement the Trigger interface:
On top of providing a concrete type for all Trigger interface's attributes, these types also have their own specific fields, like isTriggered and statement, that are specific to that particular type of trigger.
HAL interfaces are:
Trigger
Match
Action
How to query an interface
To ask for a field on a specific object type, you need to use an inline fragment:
{
allTriggers {
UUID
... on EventsTrigger {
statement {
contract {
address
abi
}
filters {
method {
name
}
type
parameter
condition {
predicate
attribute
unit
}
}
}
}
... on TransactionsTrigger {
statement {
contract {
address
abi
}
filters {
type
method {
name
}
parameter
condition {
predicate
attribute
unit
}
}
}
}
... on ContractsTrigger {
statement {
contract {
address
abi
}
method {
name
}
inputs
outputFilters {
returnIndex
condition {
predicate
attribute
unit
}
parameter
}
}
}
}
}
The second concept that you need to be familiar with is that of Union types. Please read here to fully appreciate the difference between interfaces and unions types.
For example, within HAL Outcomes you can find the Respond union type:
union Response = MailResponse | WebhookResponse | ErrorResponse
In HAL there are two union types:
response
payload
How to query a union type
In this case, if you query a field that returns the Response union type, you need to use a conditional fragment:
query { outcomes {UUID response {... on MailResponse { messageId }... on WebhookResponse { httpCode body }... on ErrorResponse { error } } }}
