I am creating app with Shopify Functions for applying discounts with Product Discount API .
The project template was taken from https://github.com/Shopify/function-examples/tree/main/sample-apps/discounts-tutorial (Code I will be talking about is placed in /extentions/volume/src/main.rs)
While developing I have noticed a bug, that discounts are not applied when cart contains 2 items of same product and same variant, but has different attributes.
Steps to reproduce the bug:
- Add the following code to /extentions/volume/src/main.rs
use std::process;
...
fn function(input: input::Input) -> Result<FunctionResult, Box<dyn std::error::Error>> {
let config: input::Configuration = input.configuration();
let cart_lines = input.cart.lines;
let mut targets = vec![];
for line in &cart_lines {
if line.attribute.is_none() == true {
continue;
}
targets.push(Target::ProductVariant { id: line.merchandise.id.as_ref().unwrap().to_string(), quantity: 1 });
}
if targets.is_empty() {
return Ok(FunctionResult {
discounts: vec![],
discount_application_strategy: DiscountApplicationStrategy::First,
});
}
eprintln!("targets: {:?}", targets);
// process::exit(1); // added for debugging
Ok(FunctionResult {
discounts: vec![Discount {
message: None,
conditions: None,
targets,
value: Value::Percentage(Percentage { value: config.percentage }),
}],
discount_application_strategy: DiscountApplicationStrategy::Maximum,
})
}
- Update CartLine in api.rs
#[derive(Clone, Debug, Deserialize)]
pub struct CartLine {
pub quantity: Int,
pub merchandise: Merchandise,
pub attribute: Option<CartLineAttribute>,
}
#[derive(Clone, Debug, Deserialize)]
pub struct CartLineAttribute {
pub value: String,
}
- Update input.graphql
query Input {
cart {
lines {
quantity
attribute(key: "YOUR_ATTRIBUTE_KEY") {
value
}
merchandise {
...on ProductVariant {
id
}
}
}
}
discountNode {
metafield(namespace: "discounts-tutorial-app", key: "function-config") {
value
}
}
} - Create discount from App
- Add product with attribute (Discount is applied)
- Add same product without attribute (Here the bug comes)
After we add product without attribute the discount is not applied at all (neither to first or second item).
I have checked that code in main.rs produces valid output by logging targets:
targets: [ProductVariant { id: "gid://shopify/ProductVariant/40125286744188", quantity: 1 }]
Possible reason for bug:
I suppose the problem is in target variant id. Currently there are 2 items in cart with same variant id. Maybe script responsible for applying discounts is failing to identify which line item should get a discount.
This does not happen if items are different, or if I increase quantity of items in cart (adding same item with attribute)
I don't know where or whom to address this issue, so I have created it here.
