---
title: "AddJoinLayer"
slug: "addjoinlayer"
updated: 2023-07-20T17:17:12Z
published: 2023-07-20T17:17:12Z
canonical: "docs.datajet.app/addjoinlayer"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.datajet.app/llms.txt
> Use this file to discover all available pages before exploring further.

# AddJoinLayer

Adds a join layer on top of an existing join between 2 tables.

| Key | Value(s) | Description |
| --- | --- | --- |
| method | "AddJoinLayer" | Adds a join layer on top of an existing join between 2 tables. |
| project | "ProjectName" | Name of current project. |
| primaryTable | "PrimaryTableName" | Required. The name of primary table. Primary and foreign tables must already be linked. |
| foreignTable | "ForeignTableName" | Required. The name of foreign table. Primary and foreign tables must already be linked. |
| primaryKey | "PrimaryKeyName" | Required. The name of the primary key. |
| foreignKey | "ForeignKeyName" | Required. The name of the foreign key. |

Use join layers to build multiple levels of join between 2 tables. Use JoinLayers Engineering Functions to summarize join details and refine selections based on specific join parameters. Before using AddJoinLayer use [AddJoin](/v1/docs/addjoin) to create the primary link between the two tables.

```json
{
  "method": "AddJoinLayer",
  "project": "Projectname",
  "primaryTable": "primaryTableName",
  "foreignTable": "foreignTableName",
  "primaryField": "primaryKeyShortName",
  "foreignField": "foreignKeyShortName"
}
```

The following shows how the JoinLayers engineering functions can be used to calculate multi-level link quality:

![](https://cdn.document360.io/73b6469b-c1e4-47e9-aa65-986c8ebd17ca/Images/Documentation/image-1689274740024.png)