# ❖ ForeignToPrimaryKeySubset

{% 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](https://docs.sdv.dev/sdv/explore/sdv-bundles/cag) page.
{% endhint %}

Use the **ForeignToPrimaryKeySubset** constraint when you have a 1-to-many connection between tables, but only certain values are allowed to have connections.

<figure><img src="https://1967107441-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FfNxEeZzl9uFiJ4Zf4BRZ%2Fuploads%2FNDP7hSnEP6enF0xY0cNc%2Fforeign-to-primary-key-subset_May%208%202025.png?alt=media&#x26;token=5ef39dc2-e6af-45f0-be1d-854402197bb5" alt=""><figcaption><p>In this example, only premium type accounts are allowed to have perks.</p></figcaption></figure>

## Constraint API

Create a `ForeignToPrimaryKeySubset`  constraint.

**Parameters**:&#x20;

* (required) `parent_table_name`: A string with the name of the parent table in the relationship
* (required) `child_table_name`: A string with the name of the child table in the relationship
* (required) `child_foreign_key`: A string with the name of the foreign key column in the child. This column is only allowed to be connected to the parent table with certain values.
* (required) `conditional_column_name`: A string with the name of the conditional column in the parent table. The values in this column determine which connections are allowed.
* (required) `conditional_values`: A list of values of the conditional column. Only these particular values are allowed to have connections with the child table.

```python
from sdv.cag import ForeignToPrimaryKeySubset

my_constraint = ForeignToPrimaryKeySubset(
    parent_table_name='Accounts',
    child_table_name='Perks',
    child_foreign_key='ID',
    conditional_column_name='Type',
    conditional_values=['PREMIUM'])
```

Make sure that all the tables and columns you provide are listed in your [Metadata](https://docs.sdv.dev/sdv/concepts/metadata), as well as the relationship between the primary and foreign key.

## 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=['ForeignToPrimaryKeySubset']
)
```

**Detection Parameters**: None


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