Tutorial: Building Shopify Functions with Rust

Shopify Functions allow developers to write custom logic that integrates directly into Shopify's backend workflows. This tutorial demonstrates how to create a Shopify Function using Rust.

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Prerequisites

1. Rust Installed:

   • Install Rust from rust-lang.org.
   • Ensure the cargo tool is available by running cargo --version.

2. Shopify CLI:

   • Install the Shopify CLI from Shopify's CLI guide.

3. GraphQL Knowledge:

   • Familiarity with GraphQL queries and schemas is beneficial.

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Setting Up Your Project

1. Initialize a New Project:

   cargo new shopify-function-example
   cd shopify-function-example
   

2. Add Dependencies: Update Cargo.toml to include Shopify-related dependencies.

   [dependencies]
   shopify_function = "0.1"
   serde = { version = "1.0", features = ["derive"] }
   serde_json = "1.0"
   decimal = "0.20"
   

3. Install Shopify CLI Extensions:

   shopify extension create --type=discount_function
   

   Follow the prompts to configure the new function.

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Writing the Function Logic

1. Define the Function: Create a new file src/main.rs with the following content:

   use shopify_function::prelude::*;
   use shopify_function::Result;
   
   #[shopify_function_target(query_path = "src/run.graphql", schema_path = "schema.graphql")]
   fn run(input: input::ResponseData) -> Result<output::FunctionRunResult> {
       let no_discount = output::FunctionRunResult {
           discounts: vec![],
           discount_application_strategy: output::DiscountApplicationStrategy::FIRST,
       };
   
       let targets = input.cart.lines
           .iter()
           .filter(|line| line.quantity >= 2)
           .map(|line| output::Target::CartLine(output::CartLineTarget {
               id: line.id.to_string(),
               quantity: None,
           }))
           .collect::<Vec<output::Target>>();
   
       if targets.is_empty() {
           eprintln!("No cart lines qualify for volume discount.");
           return Ok(no_discount);
       }
   
       Ok(output::FunctionRunResult {
           discounts: vec![output::Discount {
               message: None,
               targets,
               value: output::Value::Percentage(output::Percentage {
                   value: Decimal(10.0),
               }),
           }],
           discount_application_strategy: output::DiscountApplicationStrategy::FIRST,
       })
   }
   

2. GraphQL Schema: Create a schema.graphql file to define the input/output structure for your function:

   type Query {
       cart: Cart!
   }
   
   type Cart {
       lines: [CartLine!]!
   }
   
   type CartLine {
       id: ID!
       quantity: Int!
   }
   

3. GraphQL Query: Create a src/run.graphql file to fetch the necessary data:

   query {
       cart {
           lines {
               id
               quantity
           }
       }
   }
   

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Understanding the Code

1. Procedural Macro:

   #[shopify_function_target(query_path = "src/run.graphql", schema_path = "schema.graphql")]
   

   This macro:

   • Links your function to Shopify’s backend.
   • Ensures compliance with the provided GraphQL schema and query.

2. Filtering Logic:

   let targets = input.cart.lines
       .iter()
       .filter(|line| line.quantity >= 2)
   

   Filters cart lines where the quantity is 2 or more.

3. Applying Discounts:

   Ok(output::FunctionRunResult {
       discounts: vec![output::Discount {
           value: output::Value::Percentage(output::Percentage {
               value: Decimal(10.0),
           }),
       }],
   })
   

   Creates a 10% discount for eligible items.

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Testing Your Function

1. Build the Project:

   cargo build --release
   

2. Run Tests: Use the Shopify CLI to test the function:

   shopify extension serve
   

3. Simulate Inputs: Use the Shopify GraphQL API to simulate various cart scenarios and verify the output.

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Deploying the Function

1. Bundle the Function:

   cargo build --release
   

   Upload the target/release binary to Shopify.

2. Use Shopify CLI:

   shopify extension push
   

   Deploy the function to your Shopify store.

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Additional Resources

• Shopify Function Documentation
• Rust Programming Language
• GraphQL Official Site
• Youtube Video

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By following this guide, you’ve successfully built a Shopify Function in Rust that applies discounts based on cart line quantities. Feel free to extend this example to meet your specific business logic!