feat: Adding support to parse discriminator field in ObjectSchema

crates/oas3/src/spec/discriminator.rs

@@ -0,0 +1,57 @@
+//! 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};
+
+/// 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://spec.openapis.org/oas/v3.1.0#discriminator-object>
+#[derive(Clone, Debug, PartialEq, Default, Deserialize, Serialize)]
+pub struct Discriminator {
+    /// The name of the property in the payload that will hold the discriminator value.
+    #[serde(rename = "propertyName")]
+    pub property_name: String,
+
+    /// An 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;

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)]
@@ -526,6 +529,12 @@ pub struct ObjectSchema {
     /// See <https://github.com/OAI/OpenAPI-Specification/blob/HEAD/versions/3.1.0.md#specification-extensions>.
     #[serde(flatten, with = "spec_extensions")]
     pub extensions: BTreeMap<String, serde_json::Value>,
+
+    /// Discriminator for object selection based on propertyName
+    ///
+    /// See <https://spec.openapis.org/oas/v3.1.0#discriminator-object>
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub discriminator: Option<Discriminator>,
 }
 
 impl ObjectSchema {
@@ -628,4 +637,22 @@ 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());
+    }
 }