This is a minimal reproduction for inserting an array containing a mixture of regular strings and ISO 8601 formatted strings into a field of type String[].

As of Prisma Client v3.0.2, executing such a query throws a type validation error.

1. Starting the database with docker-compose up.
2. Apply the schema with npx prisma migrate dev
3. Seed the database with npx prisma db seed.
4. An error should be thrown.

The file prisma/seed.ts contains 4 posts:

[
  {
    id: 1,
    words: ["hello", "world"],
  },
  {
    id: 2,
    words: ["2021-09-14T00:00:00.000Z"],
  },
  {
    id: 3,
    words: ["2021-09-14T00:00:00.000Z", "2021-09-20T12:00:00.000Z"],
  },
  {
    id: 4,
    words: ["hello", "2021-09-14T00:00:00.000Z"],
  },
];

Each post contains a different mixture of regular strings and ISO 8601 formatted strings.

• Post 1 only has regular strings, this is of type List<String>
• Post 2 contains a single datetime string, this is of type List<DateTime>
• Post 3 contains multiple datetime strings, this is also of type List<DateTime>
• Post 4 contains one of each, this is of type List<String | DateTime>

The first 3 posts are inserted successfully, and only post 4 fails.