# System fields

All default, and custom content types come with some managed system fields. These fields reflect certain states of your content.

All default, and custom content types come with some managed system fields. These fields reflect certain states of your content, such as when it was last updated, or published at.

## Default model fields

These fields are included with all content models you create within Hygraph.

| Field              | Type        | Description                                        |
| ------------------ | ----------- | -------------------------------------------------- |
| `id`               | `ID!`       | Unique for each content entry                      |
| `createdAt`        | `DateTime!` | Timestamp for when the content entry was created   |
| `createdBy`        | `User`      | The user who created the content entry             |
| `updatedAt`        | `DateTime!` | Timestamp for when the content entry was updated   |
| `updatedBy`        | `User`      | The user who last updated the content entry        |
| `publishedAt`      | `DateTime!` | Timestamp for when the content entry was published |
| `publishedBy`      | `User`      | The user who last published the content entry      |
| `documentInStages` | `[model]`   | Query the current document in other stages         |

## User fields

Since the User model is included with every project, it also comes with some predefined fields, as well as all of the system fields above (but not `createdBy`, `updatedBy`, and `publishedBy`).

The User model is part of "user attribution", and is connected with content entries. This connection allows you to see who created, updated, and published content entries.

| Field         | Type        | Description                                            |
| ------------- | ----------- | ------------------------------------------------------ |
| `id`          | `ID!`       | The ID of the user                                     |
| `name`        | `String!`   | The name of the user                                   |
| `picture`     | `String`    | The profile picture URL                                |
| `kind`        | `UserKind!` | The type of user - either `MEMBER`, `PAT`, or `PUBLIC` |
| `createdAt`   | `DateTime!` | The created at date and time of the user               |
| `updatedAt`   | `DateTime!` | The last updated at date and time of the user          |
| `publishedAt` | `DateTime`  | The last published at date and time of the user        |

- If content is mutated with a [Permanent Auth Token](https://hygraph.com/docs/api-reference/basics/authorization#permanent-auth-tokens) then `kind` will return `PAT`.
- If [Public API Permissions](https://hygraph.com/docs/api-reference/basics/authorization#public-api-permissions) are enabled, and content is mutated, `kind` will return `PUBLIC`.

**Warning:**
All users will currently be members of your project. In the future they can be external users, part of a user authentication API.

  **Created by**

```graphql
{
  posts {
    createdBy {
      id
      name
      picture
      kind
    }
  }
}
```

  
  **Updated by**

```graphql
{
  posts {
    updatedBy {
      id
      name
      picture
      kind
    }
  }
}
```

  
  **Published by**

```graphql
{
  posts {
    publishedBy {
      id
      name
      picture
      kind
    }
  }
}
```


## Asset fields

Since the Asset model is included with every project, it also comes with some predefined fields, as well as all of the system fields above.

The Asset field type has all of the [default model fields](#default-model-fields), as well as:

| Field           | Type        | Description                                                                                               |
| --------------- | ----------- | --------------------------------------------------------------------------------------------------------- |
| `url`           | `String!`   | The URL of the asset, with any [transformations](https://hygraph.com/docs/api-reference/assets/transformations). |
| `handle`        | `String!`   | The file handle.                                                                                          |
| `fileName`      | `String!`   | The document file name that was uploaded.                                                                 |
| `height`        | `Float`     | The height of the file (for images only).                                                                 |
| `width`         | `Float`     | The width of the file (for images only).                                                                  |
| `size`          | `Float`     | The total file size.                                                                                      |
| `mimeType`      | `String`    | The mime type of the file.                                                                                |
| `locale`        | `Locale!`   | The system locale enumeration for your projects locales. E.g. `en`, `de`.                                 |
| `localizations` | `[Asset!]!` | An array of localized assets for the asset you are querying.                                              |

Asset fields are localized by default, and always include the localization fields described below.

**Pro Tip:**
While the Assets model is a system model that comes with every project by default and contains some predefined fields, you can still edit it to add fields for things like **alt text** and **captions** to your image assets.

Click [here](https://hygraph.com/docs/getting-started/quickstart#add-fields-to-your-model) to learn more about adding fields to a model.

## Localization fields

When you localize fields within Hygraph, the model will be updated to contain the following fields:

| Field           | Type            | Description                                                               |
| --------------- | --------------- | ------------------------------------------------------------------------- |
| `locale`        | `Locale!`       | The system locale enumeration for your projects locales. E.g. `en`, `de`. |
| `localizations` | `[modelName!]!` | An array of localized entries for the model you are querying.             |

Learn more about working with [Localization](https://hygraph.com/docs/api-reference/content-api/localization).

## Version history fields

One of the [auto-generated queries](https://hygraph.com/docs/api-reference/content-api/queries#auto-generated-queries) Hygraph will create is around versioning. Each time you publish content to a stage, a version is saved.

You can fetch the version history of a content entry by using the `history` field on a model. This field is managed automatically by Hygraph.

| Field       | Type        | Description                                                             |
| ----------- | ----------- | ----------------------------------------------------------------------- |
| `id`        | `ID!`       | The `id` of the content entry you are querying.                         |
| `stage`     | `Stage!`    | The content stage the content entry was published to. E.g. `PUBLISHED`. |
| `revision`  | `Int!`      | The revision number. Auto incrementing from `1`.                        |
| `createdAt` | `DateTime!` | The timestamp when the version was created.                             |

  **Query**

```graphql
{
  posts {
    id
    title
    history {
      id
      stage
      revision
      createdAt
    }
  }
}
```


## Connection type fields

Since Hygraph implements the Relay specification, when [fetching with Relay](https://hygraph.com/docs/api-reference/content-api/queries#fetching-with-relay) you will have some fields made available to you automatically.

For example, let's imagine we have the model `Post`. The `postsConnection` would look a little something like:

| Field       | Type           | Description                                       |
| ----------- | -------------- | ------------------------------------------------- |
| `edges`     | `[PostEdge!]!` | A list of edges, containing cursor, and the node. |
| `pageInfo`  | `PageInfo!`    | Information used for paginating nodes.            |
| `aggregate` | `Aggregate!`   | The count of records, relative to any filters.    |

### [PostEdge!]!

| Field    | Type      | Description                                                   |
| -------- | --------- | ------------------------------------------------------------- |
| `cursor` | `String!` | The edge cursor, used for paginating records.                 |
| `node`   | `Post!`   | The actual entry of the record, for example the `Post` entry. |

  **Query**

```graphql
{
  postsConnection {
    edges {
      cursor
      node {
        id
        name
      }
    }
  }
}
```

  
  **Response**

```graphql
{
  "data": {
    "postsConnection": {
      "edges": [
        {
          "cursor": "cmf1mcmbh299508ui7anmk094",
          "node": {
            "id": "cmf1mcmbh299508ui7anmk094",
            "name": "Test Hotel 1"
          }
        }
      ]
    }
  }
}
```


### PageInfo!

Hygraph exposes the `PageInfo` type on the field `pageInfo` for connection queries. This is useful with cursor based pagination.

| Field             | Type       | Description                                       |
| ----------------- | ---------- | ------------------------------------------------- |
| `hasNextPage`     | `Boolean!` | When paginating forwards, are there more items?   |
| `hasPreviousPage` | `Boolean!` | When paginating backwards, are there more items?  |
| `startCursor`     | `String`   | When paginating backwards, the cursor to continue |
| `endCursor`       | `String`   | When paginating forwards, the cursor to continue  |
| `pageSize`        | `Int`      | The number of items in the current page           |

  **Query**

```graphql
{
  postsConnection {
    pageInfo {
      hasNextPage
      hasPreviousPage
      startCursor
      endCursor
      pageSize
    }
  }
}
```
  
  **Response**

```
{
  "data": {
    "postsConnection": {
      "pageInfo": {
        "hasNextPage": false,
        "hasPreviousPage": false,
        "startCursor": "cmecw9abm00xg07t9tesgjqtr",
        "endCursor": "cmecw9abm00xg07t9tesgjqtr",
        "pageSize": 1
      }
    }
  }
}
```


Learn more about [Relay cursor pagination](https://hygraph.com/docs/api-reference/content-api/pagination#relay-cursor-connections).

### Aggregate!

It is possible using the connection type query to perform an aggregate count.

| Field   | Type   | Description                                           |
| ------- | ------ | ----------------------------------------------------- |
| `count` | `Int!` | The count of results matching the query, and filters. |

  **Query**

```graphql
query{
  postsConnection(where: {author: {name: "John Doe"}}) {
    aggregate {
      count
    }
    edges{
      node{
        __typename
        name
        id
      }
    }
  }
}
```

  
  **Response**

```graphql
{
  "data": {
    "postsConnection": {
      "aggregate": {
        "count": 5
      },
      "edges": [
        {
          "node": {
            "__typename": "Location",
            "name": "Berlin",
            "id": "cmf1mcmbh299508ui7anmk094"
          }
        },
        {
          "node": {
            "__typename": "Location",
            "name": "Madrid",
            "id": "cm3955wgx5l4v07w8qo85w6c6"
          }
        },
        {
          "node": {
            "__typename": "Location",
            "name": "New York",
            "id": "cm3ouzcvl35nx07w6fbsogx9z"
          }
        },
        {
          "node": {
            "__typename": "Location",
            "name": "Paris",
            "id": "cmbqzkn5w01dt07w6pzpkk39q"
          }
        },
        {
          "node": {
            "__typename": "Location",
            "name": "Rome",
            "id": "cmdf1xsqxt3b907wblemn6015"
          }
        }
      ]
    }
  }
}
```