GraphQL Type System

The GraphQL type system is a fundamental concept in GraphQL that defines the structure and capabilities of a GraphQL server. It plays an important role in specifying the data types used in a GraphQL application and helps define the schema, which acts as a contract between the client and the server.

In this article, We will learn about a Type System, its types, syntax, examples, and so on.

What is a GraphQL Type System?

• GraphQL is a strongly typed language, which means every piece of data in a GraphQL service has a specific type.
• It is a concept in GraphQL which is used to describe the potential of a GraphQL server.
• It helps to define the various data types which are used in a GraphQL application. With the help of Type System, it helps to define the schema, which is a contract between the client and the server.
• It tells us what data type can be queried and what are the operations which can be performed. It also informs us whether a query is valid or not.
• The type system also ensures that queries are valid and provides a clear structure for interacting with the server.

Different Types of Type System

1. Scalar Type

• These types are primitive data types. These data types tend to store only a single value.GraphQL offers various default scalar types:
• Int: Signed 32-bit Integer.
• Float: Signed number with values in integer and decimal form.
• String: UTF – 8-character sequence.
• Boolean: True or false.
• ID: It is a unique identifier that is particularly used for identifying an item or object.

Syntax:

scalar Int
scalar Float
scalar String
scalar Boolean
scalar ID

Example:

Suppose we have a schema for a blog application, and we want to define a Post type that includes a title and content, both of which are strings.

type Post {
  id: ID!
  title: String!
  content: String!
  createdAt: DateTime!
}

2. Object Type

• It is regarded as the most common type of data type which is used in a schema.
• It allow users to represent a group of fields as a whole.It also supports the nested type features in this data type.

Syntax:

type Person {
  id: ID!
  name: String!
  age: Int!
  address: Address!
}

Example:

Suppose we want to store the basic structure for storing employee information in a GraphQL schema.

--To define an object type--  
type Employee {  
   emp_id:ID  
   firstname: String  
   age: Int  
   salary:Float  
} 

–To define a GraphQL schema–

type Query  
{  
       emp_details:[Employee]  
} 

3. Query Type

• These data types are used to define the entry points for retrieving the data.
• It is among the top root-level types in GraphQL. Basically it is a request which is sent from the client to the server.

Syntax:

type Query {   
person(id: ID!): Person   
allPersons: [Person!]!
}

Example:

Suppose we want to greet message from the server in a GraphQL query.

type Query  {
   greeting: String
}

4. Mutation Type

• The Mutation Type is among the top root-level types in GraphQL.
• It is used to specify the entry point to perform the data mainpulations operations. It performs operations like create, update or delete data.

Syntax:

type Mutation {   
createPerson(name: String!, age: Int!): Person!   
updatePerson(id: ID!, name: String, age: Int): Person   
deletePerson(id: ID!): Boolean 
}

Example:

Suppose we want to add a new employee to the system.

type Mutation {  
   addEmployee(firstName: String, lastName: String): Employee  
}  

5. Enum Type

• This data type is used to represent the leaf values in a GraphQL type system.
• This data types is preferred to use where the user have a list of options to choose from. It is very much similar to the scalar type.

Syntax:

type enum_name{
val_1
val_2
}

Example:

type Days_of_Week{  
   SUNDAY  
   MONDAY  
   TUESDAY  
   WEDNESDAY  
   THURSDAY  
   FRIDAY  
   SATURDAY  
} 

6. List Type

• This data type is used to represent a collection.
• It is generally used to represent an array of values of a particular type.It is used with the type modifier to wraps similar obhects, scalar, enum etc.

Syntax:

field:[data_type]

Example:

Suppose we want to returns a list of strings, representing a to-do list.

Example:
type Query {  
   todo: [String]  
} 

7. Non-Nullable Type

• This data type has a special feature or characteristics through which it can either return a value of the specified type or it can have no value.
• To define a non-nullable type, the field must be defined with an exclamation mark(!).

Syntax:

field:data_type!

Example:

Suppose we want to define the field for the employee where the employee if can’t be NULL.

type Employee {  
   emp_id:ID!  
   firstName:String  
   lastName:String  
}  

Conclusion

The GraphQL type system is a powerful feature that allows developers to define the structure of their APIs and specify the types of data that can be queried. By understanding the different types in the GraphQL type system, developers can create flexible and efficient APIs that meet the needs of their applications.