Using Variables in GraphQL Queries

1. Introduction

In GraphQL, variables allow you to create dynamic queries that can be reused with different parameters. This lesson explores the concept of variables, their definition, usage, and best practices for implementing them in your GraphQL queries.

2. What are Variables?

Variables in GraphQL serve as placeholders for dynamic values. Instead of hardcoding values in queries, variables enable you to pass values at runtime, making your queries more flexible and efficient.

3. Defining Variables

To define a variable in a GraphQL query, you must precede the variable's name with a dollar sign ($) and declare its type. The syntax is as follows:

query GetBooks($genre: String!) {
    books(genre: $genre) {
        title
        author
    }
}
    

4. Using Variables in Queries

Once variables are defined, you can use them in your queries. Below is a practical example that demonstrates how to use variables in a GraphQL query.

query GetBooksByGenre($genre: String!) {
    books(genre: $genre) {
        title
        author
        publishedYear
    }
}
    

To execute this query, you pass the variable value alongside the query itself. For example, if you want to fetch books of the genre "Science Fiction":

{
    "query": "query GetBooksByGenre($genre: String!) { books(genre: $genre) { title author publishedYear } }",
    "variables": {
        "genre": "Science Fiction"
    }
}
    

5. Best Practices

• Always use variables for dynamic inputs to enhance security.
• Define variable types to ensure that the input conforms to the expected format.
• Keep variable names descriptive to improve query readability.
• Limit the use of optional variables unless necessary to avoid null checks.

6. FAQ