# Relationship Fields in a Header Row (2.0)

Many objects in Salesforce are related to other objects. For example, Account is a parent of Contact. You can add a reference to a related object in a CSV file by representing the relationship in a column header. When you're processing records in the Bulk API, you use `RelationshipName.IndexedFieldName` syntax in a CSV column header to describe the relationship between an object and its parent, where RelationshipName is the relationship name of the field and IndexedFieldName is the indexed field name that uniquely identifies the parent record. Use the `describeSObjects()` call in the API to get the `relationshipName` property value for a field.

Some objects also have relationships to themselves. For example, the `ReportsTo` field for a contact is a reference to another contact. If you're inserting a contact, you could use a `ReportsTo.Email` column header to indicate that you're using a contact's `Email` field to uniquely identify the `ReportsTo` field for a contact. The `ReportsTo` portion of the column header is the `relationshipName` property value for the `ReportsTo` field. The following CSV file uses a relationship:

```nolang
FirstName,LastName,ReportsTo.Email
Tom,Jones,buyer@salesforcesample.com

```

Note the following when referencing relationships in CSV header rows:

- You can use a child-to-parent relationship, but you can't use a parent-to-child relationship.
- You can use a child-to-parent relationship, but you can't extend it to use a child-to-parent-grandparent relationship.
- You can only use indexed fields on the parent object. A custom field is indexed if its `External ID` field is selected. A standard field is indexed if its `idLookup` property is set to `true`. See the Field Properties column in the field table for each [standard object](https://developer.salesforce.com/docs/atlas.en-us.object_reference.meta/object_reference/sforce_api_objects_list.htm).

## Relationship Fields for Custom Objects

Custom objects use custom fields to track relationships between objects. Use the relationship name, which ends in `__r` (underscore-underscore-r), to represent a relationship between two custom objects. You can add a reference to a related object by representing the relationship in a column header.

If the child object has a custom field with an `API Name` of `Mother_Of_Child__c` that points to a parent custom object and the parent object has a field with an `API Name` of `External_ID__c`, use the column header `Mother_Of_Child__r.External_ID__c` to indicate that you're using the parent object's `External ID` field to uniquely identify the `Mother Of Child` field. To use a relationship name in a column header, replace the `__c` in the child object's custom field with `__r`. For more information about relationships, see Understanding Relationship Names in the *Salesforce SOQL and SOSL Reference Guide* at [www.salesforce.com/us/developer/docs/soql_sosl/index.htm](https://developer.salesforce.com/docs/atlas.en-us.soql_sosl.meta/soql_sosl/).

The following CSV file uses a relationship:

```nolang
Name,Mother_Of_Child__r.External_ID__c
CustomObject1,123456
```

## Relationships for Polymorphic Fields

A polymorphic field can refer to more than one type of object as a parent. For example, either a contact or a lead can be the parent of a task. In other words, the `WhoId` field of a task can contain the ID of either a contact or a lead. Because a polymorphic field is more flexible, the syntax for the column header has an extra element to define the type of the parent object. The syntax is:

`ObjectType:RelationshipName.IndexedFieldName`.

:::important
Starting with version 57.0 of the API, for `ObjectType` use apiName, which should include namespace, if any, and should include `__c` if the object is a custom object.
:::

The following sample includes two reference fields:

1. The `WhoId` field is polymorphic and has a `relationshipName` of `Who`. It refers to a lead and the indexed `Email` field uniquely identifies the parent record.
2. The `OwnerId` field is not polymorphic and has a `relationshipName` of `Owner`. It refers to a user and the indexed `Id` field uniquely identifies the parent record.

```nolang
Subject,Priority,Status,Lead:Who.Email,Owner.Id
Test Bulk API polymorphic reference field,Normal,Not Started,lead@salesforcesample.com,005D0000001AXYz
```

:::warning
The `ObjectType:` portion of a field column header is only required for a polymorphic field. You get an error if you omit this syntax for a polymorphic field. You also get an error if you include this syntax for a field that is not polymorphic.
:::