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kind: "endpoints"
methods: [POST]
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parent: "https://agents.1health.io/public/demo/api/v3/custom-data/definition/_id_/agents.md"
html: "https://agents.1health.io/public/demo/api/v3/custom-data/definition/_id_/field/index.html"
how_to: "https://agents.1health.io/public/demo/api/v3/custom-data/definition/_id_/field/how-to.md"
use_case: "https://agents.1health.io/public/demo/api/v3/custom-data/definition/_id_/field/use-case.md"
source_version: "43d07c0335624b7661c2872315a5f184e8c3d832"
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---

# /v3/custom-data/definition/{id}/field

**URL**: https://demo.1health.io/api/v3/custom-data/definition/{id}/field

APIs for defining custom fields on a business object class. Supports creating, replacing, partially updating, and retiring definitions. The tenant and application are resolved from the authenticated context; storage slots are allocated automatically.

## Endpoints

| Endpoint | Method | Description |
| --- | --- | --- |
| /v3/custom-data/definition/{id}/field | POST | Add a custom field to a definition |

---

## POST /v3/custom-data/definition/{id}/field

Add a custom field to a definition

### Overview

**Overview**: Adds a single custom field to an existing custom data definition. The caller provides a business `displayName` and `fieldType`; the platform automatically allocates the next available storage slot for the field's attribute type.

**Behavior & Use Cases**:
- The `fieldType` must be one of the supported attribute types, matched case-insensitively: `INTEGER` (alias `INT`), `DECIMAL`, `TEXT`, `DATE`, `TIMESTAMP`, `JSON` (alias `JSONB`); unsupported types are rejected
- The lowest available storage slot for the attribute type is allocated automatically; each definition supports up to 20 fields per attribute type, except `JSON` which supports up to 3
- The request is rejected when no slots remain for the selected attribute type
- The `displayName` must be unique within the definition
- When `fieldType` is `JSON`, a provided `jsonSchema` must be well-formed JSON

**Important Notes**:
- Requires authentication; the target application is taken from the authenticated application context or from an explicit `appId` (see the `appId` parameter)
- Returns 404 when the definition does not exist for the caller's application

### Authorization

Bearer JWT required. See the [authentication guide](https://agents.1health.io/public/demo/api/authentication/agents.md).

### Path Parameters

| Parameter | Type | Required | Description |
| --- | --- | --- | --- |
| id | Long | Yes | The ID of the custom data definition to add the field to. |

### Query Parameters

| Parameter | Type | Required | Default | Description |
| --- | --- | --- | --- | --- |
| appId | Long | No |  | External application the custom data belongs to. Optional; when omitted, the application is resolved from the authenticated context. Custom data definitions belong to the application's owner tenant: creating, updating or deleting them requires being a system administrator of that owner tenant, while reading them is allowed for the owner and any tenant the application is visible to (public, or explicitly allowed for a private application). A request with neither an application context nor an explicit appId is rejected. |

### Request Body

**Content-Type**: `application/json` · **DTO**: `CustomDataFieldDefinitionRequestDTO`

```json
{
  "displayName": "example-value",
  "fieldType": "example-value",
  "jsonSchema": "example-value"
}
```

| Field | Type | Required | Constraints | Description |
| --- | --- | --- | --- | --- |
| displayName | string | Yes | Must be unique within the business object class for the caller's application. | Display name of the custom field. |
| fieldType | string | Yes | Matched case-insensitively. Accepted values: INTEGER (alias INT), DECIMAL, TEXT, DATE, TIMESTAMP, JSON (alias JSONB). | The attribute type of the custom field. |
| jsonSchema | string | No | Only applicable when fieldType is JSON; ignored for other types. Must be well-formed JSON when provided. | JSON schema used to validate values of this field. |

### Responses

#### 201 Created

Custom field added successfully.

**DTO**: `CustomDataFieldDefinitionViewDTO`

```json
{
  "id": 1001,
  "name": "example-value",
  "displayName": "example-value",
  "fieldKey": "example-value",
  "fieldType": "example-value",
  "jsonSchema": "example-value"
}
```

| Field | Type | Nullable | Description |
| --- | --- | --- | --- |
| id | Long | No | Custom field instance ID. |
| name | String | No | Sanitized bo-core name of the custom field, derived from the display name with special characters removed. Read-only; it cannot be set through the create/update APIs. |
| displayName | String | No | Display name of the custom field. |
| fieldKey | String | No | System-generated camelCase key derived from the field's name, used for programmatic lookup and search. Read-only; it cannot be set through the create/update APIs. |
| fieldType | String | No | The attribute type of the custom field. One of: INTEGER, DECIMAL, TEXT, DATE, TIMESTAMP, JSON. |
| jsonSchema | String | Yes | JSON schema used to validate values of this field, when applicable. |

#### 400 Bad Request

Invalid request. Possible causes:
• Missing required displayName or fieldType
• Unsupported fieldType
• Duplicate displayName within the definition
• No storage slots remain for the attribute type
• Invalid jsonSchema
• Missing external application context

#### 401 Unauthorized

Not authenticated — valid session required.

#### 404 Not Found

Custom data definition not found.

### Example

```bash
curl -X POST "https://demo.1health.io/api/v3/custom-data/definition/1001/field" \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" -d '{"displayName": "example-value", "fieldType": "example-value", "jsonSchema": "example-value"}'
```

---

## Navigation
Parent: https://agents.1health.io/public/demo/api/v3/custom-data/definition/_id_/agents.md · Site guide: https://agents.1health.io/public/demo/api/agents.md