Concepts

Overview

This page explains a number of important concepts to be aware of when working with the Prisma API.

Unless otherwise stated, the examples on this page are based on a Prisma API with the following datamodel:

type User {
  id: ID! @unique
  email: String @unique
  name: String!
  posts: [Post!]!
}

type Post {
  id: ID! @unique
  title: String!
  published: Boolean! @default(value: "false")
  author: User
}

Prisma GraphQL schema

The Prisma database is the GraphQL schema defining the data types and operations of a Prisma API. It is auto-generated and specifies CRUD and realtime operations for the models specified in the service's datamodel.

Node selection

Many operations in the Prisma API only affect a subset of the existing nodes, sometimes only a single node, such as updating or deleting nodes.

In these case, you need a way to ask for specific nodes in the API. This is what the where filter argument is being used for. It lets you specify conditions for selecting the nodes to which an operation should be applied.

Nodes can be selected via any field that's annotated with the @unique directive.

Here are a few scenarios where node selection is required.

Retrieve a single User node by its email:

query {
  user(where: { email: "alice@prisma.io" }) {
    id
  }
}

{
  "data": {
    "user": {
      "id": "cjkawhcz44a4c0a84un9a86wt"
    }
  }
}

Update the title of a single Post node:

mutation {
  updatePost(
    where: { id: "ohco0iewee6eizidohwigheif" }
    data: { title: "GraphQL is awesome" }
  ) {
    id
  }
}

{
  "data": {
    "updatePost": {
      "id": "ohco0iewee6eizidohwigheif"
    }
  }
}

Update published of a many Post nodes at once (also see Batch mutations):

mutation {
  updateManyPosts(
    where: {
      id_in: [
        "ohco0iewee6eizidohwigheif"
        "phah4ooqueengij0kan4sahlo"
        "chae8keizohmiothuewuvahpa"
      ]
    }
    data: { published: true }
  ) {
    count
  }
}

{
  "data": {
    "updateManyPosts": {
      "count": 3
    }
  }
}

Batch mutations

One application of the node selection concept are the batch mutations exposed by the Prisma API. Batch updating or deleting is optimized for making changes to a large number of nodes. As such, these mutations only return how many nodes have been affected, rather than full information on specific nodes.

For example, the mutations updateManyPosts and deleteManyPosts provide a where argument to select specific nodes, and return a count field with the number of affected nodes (see the example above).

mutation {
  deleteManyUsers(where: { email_in: ["alice@prisma.io", "bob@prisma.io"] }) {
    count
  }
}

{
  "data": {
    "deleteManyUsers": {
      "count": 2
    }
  }
}

Connections (Relay Pagination & Aggregations)

Prisma offers two approaches to retrieve a list of nodes via a relation field:

• Simple relation queries (direct node retrieval):

  query {
    posts {
      id
      title
      published
    }
  }
  

• Connections queries:

  query {
    postsConnection {
      edges {
        node {
          id
          title
          published
        }
      }
    }
  }
  

In contrast to the simple relation queries that directly return a list of nodes, connection queries are based on the Relay Connection model. In addition to pagination information, connections in the Prisma API also have advanced features, like aggregation.

For example, while the posts query allows you to select specific Post nodes, sort them by some field and paginate over the result, the postsConnection query additionally allows you to count all unpublished posts:

query {
  postsConnection {
    # `aggregate` allows to perform common aggregation operations
    aggregate {
      count
    }
    edges {
      # each `node` refers to a single `Post` node
      node {
        title
      }
    }
  }
}

{
  "data": {
    "postsConnection": {
      "aggregate": {
        "count": 1
      },
      "edges": [
        {
          "node": {
            "title": "Watch all the talks from GraphQL Europe: bit.ly/gql-eu"
          }
        }
      ]
    }
  }
}

Check this feature request to learn about the upcoming aggregation operations.

Transactions & Nested mutations

For the MySQL and PostgreSQL database connectors, single mutations in the Prisma API that are not batch operations are always executed transactionally (ACID compliant), even if they consist of many actions that potentially spread across multiple related nodes. This is also true for nested mutations that perform several database writes on multiple types.

Nested mutations are mutations that are touching at least two nodes, each of a different type. Here is a simple example:

mutation {
  createUser(
    data: {
      name: "Sarah"
      posts: {
        create: [
          { title: "GraphQL is great" }
          { title: "Prisma is a data access layer" }
        ]
        connect: [{ id: "cjk1e3t7i1ark0b299pvrge5m" }]
      }
    }
  ) {
    id
    posts {
      id
    }
  }
}

This mutation touches four nodes in total:

• It creates one new User node.
• It creates two Post nodes. Both Post nodes are also directly connected to the new User node.
• It connects the new User node with one existing Post node.

This mutation performs six single actions in total:

• Creating one User node.
• Creating two Post nodes.
• Connecting three Post nodes to the new User node.

If any of the mentioned actions fail (for example because of a violated @unique field constraint), the entire mutation is rolled back!

For the SQL connectors, mutations are transactional and ACID compliant, meaning they are atomic, consistent, isolated and durable. This means that between two separate actions of the same nested mutation, no other mutations can alter the data. Also the result of a single action cannot be observed until the complete mutation has been processed.

Cascading deletes

Prisma supports different deletion behaviours for relations in your datamodel. There are two major deletion behaviours:

• CASCADE: When a node with a relation to one or more other nodes gets deleted, these nodes will be deleted as well.
• SET_NULL: When a node with a relation to one or more other nodes gets deleted, the fields referring to the deleted node are set to null.

As mentioned above, you can specify a dedicated deletion behaviour for the related nodes. That's what the onDelete argument of the @relation directive is for.

Consider the following example:

type User {
  id: ID! @unique
  comments: [Comment!]! @relation(name: "CommentAuthor", onDelete: CASCADE)
  blog: Blog @relation(name: "BlogOwner", onDelete: CASCADE)
}

type Blog {
  id: ID! @unique
  comments: [Comment!]! @relation(name: "Comments", onDelete: CASCADE)
  owner: User! @relation(name: "BlogOwner", onDelete: SET_NULL)
}

type Comment {
  id: ID! @unique
  blog: Blog! @relation(name: "Comments", onDelete: SET_NULL)
  author: User @relation(name: "CommentAuthor", onDelete: SET_NULL)
}

Let's investigate the deletion behaviour for the three types:

• When a User node gets deleted,

  • all related Comment nodes will be deleted.
  • the related Blog node will be deleted.

• When a Blog node gets deleted,

  • all related Comment nodes will be deleted.
  • the related User node will have its blog field set to null.

• When a Comment node gets deleted,

  • the related Blog node continues to exist and the deleted Comment node is removed from its comments list.
  • the related User node continues to exist and the deleted Comment node is removed from its comments list.

You can find more detailled info about the @relation directive and its usage here.

Authentication

A Prisma API can be protected with the service secret (specified as the secret property) in your prisma.yml:

secret: my-secret-42

As the developer of a Prisma service, you can choose your own service secret. When a service gets deployed with a prisma.yml that contains the secret property, the Prisma API of that service will require authentication via a service token (JWT):

The easiest way to obtain a service token is by running the prisma token command inside the same directory where your prisma.yml is located:

$ prisma token
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJkYXRhIjp7InNlcnZpY2UiOiJkZW1vQGRldiIsInJvbGVzIjpbImFkbWluIl19LCJpYXQiOjE1MzI1ODgzNzAsImV4cCI6MTUzMzE5MzE3MH0.Nv8coqsiwdwoSfWCBJHYfnr0WK2GRyqO5xTN6Q3IVkw

The generated token needs to be attached to the Autorization header of the HTTP requests made to the Prisma API:

curl '__YOUR_PRISMA_ENDPOINT__' \
-H 'Content-Type: application/json' \
-H 'Authorization: Bearer __YOUR_SERVICE_TOKEN__' \
--data-binary '{"query":"mutation { createUser(data: { name: "Sarah" }) { id } }"'