feat: Adding support to parse discriminator field in ObjectSchema (#138)

Co-authored-by: Rob Ede <[email protected]>

.vscode/settings.json

@@ -18,6 +18,7 @@
         "refpath",
         "reqwest",
         "rustfmt",
+        "rustup",
         "semver",
         "serde",
         "spdx",

crates/oas3/CHANGELOG.md

@@ -5,6 +5,8 @@
 - Add `spec::ObjectSchema::deprecated` field.
 - Add `spec::ObjectSchema::examples` field.
 - Add `spec::Contact::validate_email()` method.
+- Add `spec::Discriminator` type.
+- Add `spec::ObjectSchema::discriminator` field.
 - Expose the `spec::ClientCredentialsFlow::token_url` field.
 - The type of the `spec::ObjectSchema::enum` field is now `Vec<serde_json::Value>`.
 - The type of the `spec::ObjectSchema::const` field is now `Option<serde_json::Value>`.

crates/oas3/src/spec/discriminator.rs

@@ -0,0 +1,60 @@
+//! Schema specification for [OpenAPI 3.1](https://github.com/OAI/OpenAPI-Specification/blob/HEAD/versions/3.1.0.md)
+
+use std::collections::BTreeMap;
+
+use serde::{Deserialize, Serialize};
+
+/// A discriminator object can be used to aid in serialization, deserialization, and validation when
+/// payloads may be one of a number of different schemas.
+///
+/// The discriminator is a specific object in a schema which is used to inform the consumer of the
+/// document of an alternative schema based on the value associated with it.
+///
+/// See <https://github.com/OAI/OpenAPI-Specification/blob/HEAD/versions/3.1.0.md#discriminator-object>.
+#[derive(Debug, Clone, PartialEq, Default, Deserialize, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct Discriminator {
+    /// Name of the property in the payload that will hold the discriminator value.
+    pub property_name: String,
+
+    /// Object to hold mappings between payload values and schema names or references.
+    ///
+    /// When using the discriminator, inline schemas will not be considered.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub mapping: Option<BTreeMap<String, String>>,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn discriminator_property_name_parsed_correctly() {
+        let spec = "propertyName: testName";
+        let discriminator = serde_yml::from_str::<Discriminator>(spec).unwrap();
+        assert_eq!("testName", discriminator.property_name);
+        assert!(discriminator.mapping.is_none());
+    }
+
+    #[test]
+    fn discriminator_mapping_parsed_correctly() {
+        let spec = indoc::indoc! {"
+            propertyName: petType
+            mapping:
+              dog: '#/components/schemas/Dog'
+              cat: '#/components/schemas/Cat'
+              monster: 'https://gigantic-server.com/schemas/Monster/schema.json'
+        "};
+        let discriminator = serde_yml::from_str::<Discriminator>(spec).unwrap();
+
+        assert_eq!("petType", discriminator.property_name);
+        let mapping = discriminator.mapping.unwrap();
+
+        assert_eq!("#/components/schemas/Dog", mapping.get("dog").unwrap());
+        assert_eq!("#/components/schemas/Cat", mapping.get("cat").unwrap());
+        assert_eq!(
+            "https://gigantic-server.com/schemas/Monster/schema.json",
+            mapping.get("monster").unwrap()
+        );
+    }
+}

crates/oas3/src/spec/mod.rs

@@ -13,6 +13,7 @@ mod components;
 mod contact;
 mod encoding;
 
+mod discriminator;
 mod error;
 mod example;
 mod external_doc;
@@ -38,6 +39,7 @@ mod tag;
 pub use self::{
     components::*,
     contact::*,
+    discriminator::*,
     encoding::*,
     error::Error,
     example::*,

crates/oas3/src/spec/schema.rs

@@ -5,7 +5,10 @@ use std::{collections::BTreeMap, fmt};
 use derive_more::derive::{Display, Error};
 use serde::{Deserialize, Deserializer, Serialize};
 
-use super::{spec_extensions, FromRef, ObjectOrReference, Ref, RefError, RefType, Spec};
+use super::{
+    discriminator::Discriminator, spec_extensions, FromRef, ObjectOrReference, Ref, RefError,
+    RefType, Spec,
+};
 
 /// Schema errors.
 #[derive(Debug, Clone, PartialEq, Display, Error)]
@@ -498,6 +501,12 @@ pub struct ObjectSchema {
     // #########################################################################
 
     //
+    /// Discriminator for object selection based on propertyName
+    ///
+    /// See <https://github.com/OAI/OpenAPI-Specification/blob/HEAD/versions/3.1.0.md#discriminator-object>
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub discriminator: Option<Discriminator>,
+
     /// A free-form property to include an example of an instance for this schema.
     ///
     /// To represent examples that cannot be naturally represented in JSON or YAML, a string value
@@ -628,4 +637,24 @@ mod tests {
         let schema = serde_yml::from_str::<ObjectSchema>(spec).unwrap();
         assert_eq!(schema.example, Some(serde_json::Value::Null));
     }
+
+    #[test]
+    fn discriminator_example_is_parsed_correctly() {
+        let spec = indoc::indoc! {"
+          oneOf:
+            - $ref: '#/components/schemas/Cat'
+            - $ref: '#/components/schemas/Dog'
+            - $ref: '#/components/schemas/Lizard'
+            - $ref: 'https://gigantic-server.com/schemas/Monster/schema.json'
+          discriminator:
+            propertyName: petType
+            mapping:
+              dog: '#/components/schemas/Dog'
+              monster: 'https://gigantic-server.com/schemas/Monster/schema.json'
+        "};
+        let schema = serde_yml::from_str::<ObjectSchema>(spec).unwrap();
+
+        assert!(schema.discriminator.is_some());
+        assert_eq!(2, schema.discriminator.unwrap().mapping.unwrap().len());
+    }
 }

tests/samples.rs

@@ -15,7 +15,7 @@ fn validate_passing_samples() {
 #[test]
 fn validate_failing_samples() {
     // TODO: implement validation for one-of: [paths, components, webhooks]
-    // see https://spec.openapis.org/oas/v3.1.0#openapi-document
+    // see https://github.com/OAI/OpenAPI-Specification/blob/HEAD/versions/3.1.0.md#openapi-document
     // oas3::from_str(include_str!("samples/fail/no_containers.yaml")).unwrap_err();
 
     // TODO: implement validation for non-empty server enum