Add Create Union Type Of Nearly Identical Objects as a Zod TIL

zod/create-union-type-of-nearly-identical-objects.md

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+# Create Union Type Of Nearly Identical Objects
+
+Let's say I have a data layer that can return data in two nearly identical
+shapes. Either shape has all of the same keys except one has an `_id` key and
+the other has a `key` key. I want a Zod schema that can validate either of
+these shapes and produce a union type.
+
+Let's start with an intermediate Zod object that holds all possible keys.
+
+```typescript
+const intermediateObject = z.object({
+  _id: z.string(),
+  key: z.string(),
+  name: z.string(),
+  age: z.number()
+  // any other shared keys
+})
+```
+
+I can then manipulate this into the desired schema using
+[`or()`](https://github.com/colinhacks/zod#unions) and
+[`omit()`](https://github.com/colinhacks/zod#pickomit).
+
+```typescript
+const objectWithoutId = intermediateObject.omit({ _id: true })
+const objectWithoutKey = intermediateObject.omit({ key: true })
+
+const unionSchema = objectWithoutId.or(objectWithoutKey)
+```
+
+And this produces the schema and union type I was looking for:
+
+```typescript
+type Union = z.infer<typeof unionSchema>;
+/*
+type Union = {
+    key: string;
+    name: string;
+    age: number;
+} | {
+    _id: string;
+    name: string;
+    age: number;
+}
+*/
+```
+
+[source](https://twitter.com/jbrancha/status/1572357904266850305)