---
title: "Rules and validation"
url: https://developers.dagio.ai/rules/
---

# Rules and validation

   
                             
                                                                    
             
              
          
   

## Declare a condition

Rules express conditions on values, relations or Query results. The Model uses them for validation, Action availability or transitions. Views present the decision without becoming a second business authority.

| Condition | Expected values | Purpose |
| --- | --- | --- |
| Presence | Field reference | Check required information |
| Comparison | Field, admitted operator and typed value | Compare an amount or status |
| Membership | Field and admitted values | Accept several states |
| Relation | Type, direction and cardinality | Require a linked client |
| Query | Declared Query and admitted parameters | Check a collection or aggregate |
| Combination | Bounded boolean expressions | Combine conditions |

## Useful messages

A failed rule explains what is missing and where to correct it. “Select a client before finalizing” guides the user. Contract names or technical errors do not replace that message.

## Example

Finalizing a quote requires a linked client, positive amount and approval. The record can show missing conditions, but the service checks again at confirmation. A disabled button is not an authorization control.

Expression trees are declarative and bounded. Their [reference](https://developers.dagio.ai/reference/workspace-rule/) describes admitted variants; rules do not execute JavaScript or SQL supplied by a view.

<!-- surface-examples:start -->

## Applied examples : Check before confirming

One rule requires a company; another rejects a zero or negative amount.

### Configuration

Fragment placed in `rules[]`. [Properties and accepted values](https://developers.dagio.ai/reference/workspace-model-foundation/).

```json
{
  "contract": "WorkspaceRule@1",
  "key": "company-required",
  "label": "Company provided",
  "expression": {
    "kind": "present",
    "field": {
      "definitionPath": "workspace/clients/surface/client",
      "fieldKey": "company"
    }
  }
}
```

### Variation and connection

Fragment placed in `rules[]`. [Properties and accepted values](https://developers.dagio.ai/reference/workspace-model-foundation/).

```json
{
  "contract": "WorkspaceRule@1",
  "key": "positive-amount",
  "label": "Positive amount",
  "expression": {
    "kind": "compare",
    "field": {
      "definitionPath": "workspace/quotes/surface/quote",
      "fieldKey": "amount"
    },
    "operator": "gt",
    "value": 0
  }
}
```

### UI layout example

The illustrative layout below places this configuration in the Clients/Quotes app. Insert each fragment at the stated location, with Field, Query and Action references matching the Model declarations.

1. Company *
2. Status *
3. Notes
4. Create client

<!-- surface-examples:end -->