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104 lines
4.5 KiB
104 lines
4.5 KiB
1 year ago
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---
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title: "Links"
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description: "Understanding Link Columns!"
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---
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### Supported relationship types:
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- One to many
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- A Table record in first table is related to more than one record of second table. But second table record maps to only one entry of first table
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- NocoDB refers to this category of relationship as **has many**
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- For every **has many** relation defined, NocoDB augments **belongs to** relationship column in the adjacent table automatically
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- Example: Country **has many** Cities. (other way mapping > City **belongs to** Country )
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- Many to many
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- A Table record in first table is related to more than one record of second table; second table record can also map to more than on record of first table.
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- NocoDB refers to this category of relationship as **many to many**
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- For every **many to many** relation defined between tables, NocoDB augments **many to many** relationship column in the other table automatically
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- Example: Film **has many** Actors. Actor **has many** Films (works on many films)
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Further details of relationship types can be found [here](https://afteracademy.com/blog/what-are-the-different-types-of-relationships-in-dbms)
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From Release v0.110.0, table records can be connected through relationships using the **Links** column type.
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It is important to note that, earlier supported column type **LinkToAnotherRecord** for creating relations is considered deprecated. While the old datatype is still supported for backward compatibility, it is no longer possible to create new fields of that type.
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The main distinction between these two column types lies in how the contents are displayed within the cell when links are established between two tables. With the **LinkToAnotherRecord** column type, the cell displays the **Primary value** of the related records. On the other hand, the **Links** column type only shows the **count** of related records.
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The decision to switch over to new column type was made to ensure better performance and scalability of the application, more so when the records & the number of records in the related table is large.
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Child list to display the related records can be accessed by clicking on the link count displayed on the cell.
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Except for the column type, the following procedures remain same as before
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- Create, update & delete a relationship column,
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- Link & unlink a record,
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- Create a lookup and rollup columns
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Workflow details are captured below.
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## Adding a relationship
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1. Create column
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Click on '+' button at end of column headers
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2. Update column name
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Input name in the text box provided
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3. Select column type
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Select Column type as "Links" from the drop-down menu
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4. Choose relationship type
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- 'Has Many' corresponds to the 'One-to-many' relationships
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- 'Many To Many' corresponds to the 'Many-to-many' relationships
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5. Select child table from drop down menu
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6. Click on 'Save'
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A new column will get created in both the parent table & child table
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## Linking records
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### 1. Open link record tab
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Click on the '+' icon in corresponding row - cell
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### 2. Select from the option displayed
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Use 'Filter box' to narrow down on search items.
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You can opt to insert a new record as well, using "+ New Record" button.
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You can use `ALT + Click` to insert multiple options together.
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### 3. Column display for "Has Many" relationship
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Country 'has many' City
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Display remains similar for "Many to Many" relationship as well
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### 4. Column display for "Belongs to" relationship [Automatically updated]
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City 'belongs to' Country.
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Note: Primary value is still used as cell display value for "Belongs to" as it can have only one associated record.
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## Unlinking records
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1. Click on link count to open Child modal
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2. Click on Unlink icon against required item
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## Link label reconfiguration
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Use column edit menu for **Links** to reconfigure display label
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