# ❖ Polymorphic Relationship

{% hint style="info" %}
❖ **SDV Enterprise Bundle**. This feature is available as part of the **CAG Bundle**, an optional add-on to SDV Enterprise. For more information, please visit the [CAG Bundle](/sdv/explore/sdv-bundles/cag.md) page.
{% endhint %}

Use the **PolymorphicRelationship** constraint when the values inside a foreign key column can refer to different tables, depending on the context.

<figure><img src="/files/yi975Hy1R5y4MP8tDp9f" alt=""><figcaption><p>In this example, the <code>Transaction Log</code> table has a foreign key called <code>Details</code>. Sometimes, it refers to the <code>Debit Accounts</code> table and sometimes it refers to the <code>Credit Accounts</code> tables.</p></figcaption></figure>

## Constraint API

Create a `PolymorphicRelationship`  constraint.

**Parameters**:&#x20;

* (required) `table_name`: A string with the name of the table that contains the foreign key column
* (required) `foreign_key_column_name`: A string with the name of the foreign key column inside the table
* (required) `parent_table_names`: A list of strings containing the possible different parent tables that the foreign key column could be referring to
* `type_column_name`: Sometimes, the table may have a categorical column that controls which tables the foreign key refers to. In this case, provide a string with the name of this column.
* `type_value_to_table`: If there is a type column, provide a dictionary that maps each categorical value of the column to the table it refers to.

```python
from sdv.cag import PolymorphicRelationship

my_constraint = PolymorphicRelationship(
    table_name='Transaction Log',
    foreign_key_column_name='Details',
    parent_table_names=['Debit Accounts', 'Credit Accounts'],
    type_column_name='Type',
    type_value_to_table={
        'CREDIT': 'Credit Accounts',
        'DEBIT': 'Debit Accounts'
    }
)
```

Make sure that all the tables and columns you provide are listed in your [Metadata](/sdv/concepts/metadata.md). The table relationships will not be part of the metadata, as a polymorphic relationship cannot be inputted into the metadata.

## Usage

Apply the constraint to any SDV synthesizer. Then fit and sample as usual.

```python
synthesizer = HSASynthesizer(metadata)
synthesizer.add_constraints([my_constraint])

synthesizer.fit(data)
synthetic_data = synthesizer.sample()
```

For more information about using predefined constraints, please see the [**Constraint-Augmented Generation tutorial**](https://colab.research.google.com/drive/1WCMQujfVKL5giULZXOPPIBoMfzR9Zj68?usp=sharing).

## Auto-Detection

Auto-detection is allowed for this constraint but it is not enabled by default.

If you'd like to auto-detect this constraint specifically, you can supply it in the auto-detection parameters. This will detect all instances of the constraint throughout the dataset.

```python
constraints = synthesizer.detect_constraints(
    data,
    constraint_classes=['PolymorphicRelationship']
)
```

**Detection Parameters**: None


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