Modifying a user-defined type (UDT)

User Defined Types (UDTs) in Cassandra allows users to create custom data types. With UDTs, you can manage and organize data when multiple data fields are grouped together in a single column. In this article, we will discuss how to modify UDTs in Cassandra with the help of CQL examples.

User Defined Data (UDT)

It has the ability to attach multiple data fields in a single column. UDTs play an important role in that they can group together related fields of data (such as field 1, field 2, etc.) and allow names and types. UDT helps to add flexibility to your tables and data model. We can construct a UDT provided by Cassandra: UDT, which stands for User-Defined Type.

Creating a user-defined type (UDT)

There are many data fields. These can be combined into a single column. These include names, valid types, collections, and other existing UDTs. After creating the table the UDT can be used to define the columns in it.

To create and modify a UDT in Cassandra, you need to specify the key location where you want to create it, and then use the CREATE TYPE command followed by the name of your new type and the fields you want to include, along with their data types. Here's an example −

CREATE TYPE cycling.basic_info (
   birthday timestamp,
   nationality text,
   weight text,
   height text
);

This creates a new UDT called `basic_info` with four fields: `birthday`, `nationality`, `weight`, and `height`, each with their own data type.

Modifying a User Defined Type

After creating it, you can modify it whenever you want. There are several ways to modify a UDT in Cassandra.

Adding a New Field to a UDT

To do this, you can use the ALTER TYPE command with the ADD keyword. Here's an example:

ALTER TYPE cycling.basic_info ADD email text;

This adds a new field called `email` to the `basic_info` UDT with the `text` data type.

Removing a Field from a UDT

To do this, you can use the ALTER TYPE command with the DROP keyword. Here's an example

ALTER TYPE cycling.basic_info DROP weight;

This removes the `weight` field from the `basic_info` UDT.

Changing the Data Type of a Field in a UDT

To do this, you can use the ALTER TYPE command with the ALTER keyword. Here's an example

ALTER TYPE cycling.basic_info ALTER birthday TYPE date;

Renaming a Field in a UDT

To do this, you can use the ALTER TYPE command with the RENAME keyword. Here's an example

ALTER TYPE cycling.basic_info RENAME height TO height_cm;

This renames the `height` field to `height_cm`.

Dropping a User-Defined Type (UDT):

If you no longer need a UDT, you can drop it using the DROP TYPE command. Here's an example

DROP TYPE cycling.basic_info;

This removes the basic_info UDT from the cycling keyspace.

Some more examples

Here are some more examples of how to modify User-Defined Types (UDTs) in Cassandra using CQL

Example-1: Adding a Nested UDT to an Existing UDT:

You can also add nested UDTs to existing UDTs. Here is an example of how to add a new field to the `basic_Info` UDT which is itself a UDT:

CREATE TYPE cycling.address (
   street text,
   city text,
   state text,
   zip text
);

ALTER TYPE cycling.basic_info ADD home_address FROZEN<cycling.address>;

This creates a new UDT named `address`. Then it adds a new field called `home_address` to the `basic_information` UDT which uses the `address` UDT as its data type. Note that we use the `frozen` keyword to specify that the `address` UDT should be treated as a single, immutable object when stored in the `home_address` field.

Example-2: Changing the Name of a UDT

You can rename a UDT using the RENAME TYPE command. Here's an example

RENAME TYPE cycling.basic_info TO rider_info;

This renames the Basic_Info UDT to Rider_Info. Note that any tables or other UDTs that reference basic_info will need to be updated to reference rider_info instead.

Example-3: Updating a Nested Field in a UDT

If you are using nested UDTs and you want to update a field within the nested UDT, you must update the entire UDT using the REPLACE command. Here's an example

INSERT INTO cycling.cyclist_stats (id, lastname, basics)
VALUES (
   uuid(),
   'Froome',
   {
      birthday: '1985-05-20',
      nationality: 'British',
      weight: '68',
      height: '185',
      home_address: {
         street: '123 Main St',
         city: 'London',
         state: 'England',
         zip: 'SW1A 1AA'
      }
   }
);

UPDATE cycling.cyclist_stats
SET basics = {
   birthday: '1985-05-20',
   nationality: 'British',
   weight: '68',
   height: '185',
   home_address: {
      street: '456 Main St',
      city: 'Manchester',
      state: 'England',
      zip: 'M1 1AA'
   }
}
WHERE id = <some-uuid>;

This inserts a new row into the `cyclist_stats` table with the nested UDT (`home_address`) and then updates the `home_address` field with a new address. Note that we use the `REPLACE` command to update the entire UDT, because Cassandra treats UDTs as opaque blobs that can only be updated as a whole.

Conclusion

User Defined Types (UDTs) are a powerful feature in Cassandra. UDT allows users to create custom data types. You can group multiple data fields together in a single column. It makes it easy to manage and organize data. We have discussed how to modify a UDT in Cassandra, including adding and deleting fields, changing the data type of a field, renaming a field, and dropping a UDT in this article. With these tools, you can modify your UDT to meet your changing data requirements.