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---
lang: en
title: 'API docs: repository.hasonedefinition'
keywords: LoopBack 4.0, LoopBack 4, Node.js, TypeScript, OpenAPI
sidebar: lb4_sidebar
editurl: https://github.com/loopbackio/loopback-next/tree/master/packages/repository
permalink: /doc/en/lb4/apidocs.repository.hasonedefinition.html
---
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[Home](./index.md) > [@loopback/repository](./repository.md) > [HasOneDefinition](./repository.hasonedefinition.md)
## HasOneDefinition interface
**Signature:**
```typescript
export interface HasOneDefinition extends RelationDefinitionBase
```
**Extends:** [RelationDefinitionBase](./repository.relationdefinitionbase.md)
## Properties
| Property | Modifiers | Type | Description |
| --- | --- | --- | --- |
| [keyFrom?](./repository.hasonedefinition.keyfrom.md) | | string | _(Optional)_ |
| [keyTo?](./repository.hasonedefinition.keyto.md) | | string | <p>_(Optional)_ keyTo: The foreign key used by the target model for this relation. keyFrom: The source key used by the source model for this relation.</p><p>E.g. when a Customer has one Address instance, then keyTo is "customerId". Note that "customerId" is the default FK assumed by the framework, users can provide a custom FK name by setting "keyTo". And Customer.id is keyFrom. keyFrom defaults to the id property of a model. Users can provide a custom source key name by setting "keyTo".</p> |
| [polymorphic?](./repository.hasonedefinition.polymorphic.md) | | boolean \| { discriminator: string; } | _(Optional)_ The polymorphism of the target model. The discriminator is a key of source model. If the target model is not polymorphic, then the value should be left undefined or false; If the key on source model indicating the concrete class of the target instance is default i.e. camelCase(classNameOf(throughModelInstance)) + "Id" Then the discriminator field can be undefined |
| [targetsMany](./repository.hasonedefinition.targetsmany.md) | | false | |
| [type](./repository.hasonedefinition.type.md) | | [RelationType.hasOne](./repository.relationtype.md) | |