One of the most essential parts of effectively working with Microsoft Azure Cosmos DB in the scope of the DP-420 exam is learning how to implement user-defined functions (UDFs).
User-defined functions in Cosmos DB are written in JavaScript and they provide a way to perform transformations or calculations as part of your SQL queries. They can be directly written inline in the SQL query or can be registered with Cosmos DB and invoked by a simple function call.
User-Defined Function Syntax
A user-defined function takes the form of a JavaScript function. Here is an example:
function (input) {
// perform operations on the input
return result;
}
The ‘input’ serves as the parameter for the function, upon which operations are performed, and then the result is returned.
Creating a User-Defined Function
Implementing a user-defined function in Microsoft Azure Cosmos DB involves the following steps:
- Navigate to your Cosmos DB account in the Azure portal.
- In the left-hand menu, click on ‘Data Explorer’.
- Expand the database and the collection where you want to add the UDF.
- Click ‘New User Defined Function’.
- In the ‘New User Defined Function’ panel that appears, enter a unique Id for the UDF.
- In the function area, write the function in JavaScript and then click ‘Save’.
For example, here is how you would define a UDF that multiplies an input by 5:
{
“id”: “multiplyByFive”,
“userDefinedFunction”: {
“body”: “function (value) { return value * 5; }”
}
}
Using a User-Defined Function in a Query
Once you’ve defined a UDF, you can use it within your SQL queries in Azure Cosmos DB.
The following SQL query uses the ‘multiplyByFive’ UDF defined earlier to multiply the ‘quantity’ property of each document in a collection:
SELECT VALUE udf.multiplyByFive(r.quantity) FROM root r
Here, `udf.multiplyByFive` is the UDF function call, and `r.quantity` is the argument passed to the UDF function.
UDFs are invoked by their Id, preceded by ‘udf.’ and followed by the argument that the function should take in parentheses.
Conclusion
Understanding how to define and implement user-defined functions in Cosmos DB permits a higher level of versatility in your data operations when using Microsoft Azure Cosmos DB. It strengthens your skill set while preparing for the DP-420 exam, and furthermore, it provides valuable knowledge that you can apply in designing and implementing native applications using Microsoft Azure Cosmos DB in a real-world setting.
Practice Test
True or False: User-defined functions in Azure Cosmos DB are written using JavaScript.
- True
- False
Answer: True
Explanation: Azure Cosmos DB natively supports JavaScript for writing user-defined functions (UDFs), triggers, and stored procedures.
What method is used to implement a user-defined function (UDF) in Azure Cosmos DB?
- a) CREATE FUNCTION
- b) UPLOAD FUNCTION
- c) REPLACE FUNCTION
- d) None of the above
Answer: d) None of the above
Explanation: In Azure Cosmos DB, User-Defined Functions (UDFs) are implemented as JavaScript functions and are registered with Cosmos DB using the Cosmos DB SDK or portal, not with a specific command.
True or False: The user-defined functions in Azure Cosmos DB support usage of external packages.
- True
- False
Answer: False
Explanation: The user-defined functions in Azure Cosmos DB do not support the use of external packages or libraries other than the JavaScript standard library.
Can user-defined functions (UDFs) alter data inside Cosmos DB?
- a) Yes
- b) No
Answer: b) No
Explanation: UDFs in Azure Cosmos DB are read-only and cannot perform any write operations on data.
The user-defined functions (UDFs) in Azure Cosmos DB can return which types of results?
- a) A single value
- b) An array of results
- c) Both of the above
- d) None of the above
Answer: c) Both of the above
Explanation: UDFs in Azure Cosmos DB can return a single value or an array of results.
True or False: User-defined functions in Cosmos DB do not have access to current item in the enclosing scope.
- True
- False
Answer: True
Explanation: UDFs in Azure Cosmos DB do not have access to the current item (like triggers and stored procedures do).
User-defined functions in Azure Cosmos DB can use which database operations?
- a) Create
- b) Read
- c) Update
- d) Delete
Answer: b) Read
Explanation: UDFs in Azure Cosmos DB are read-only in nature and can only perform read operations.
How many input parameters can user-defined functions in Azure Cosmos DB have?
- a) No limit
- b) Up to 10
- c) Only 1
- d) Up to 5
Answer: a) No limit
Explanation: UDFs in Azure Cosmos DB can have any number of input parameters.
True or False: User-defined functions in Azure Cosmos DB can be executed in a pre or post-trigger.
- True
- False
Answer: False
Explanation: Triggers can call UDFs but UDFs themselves cannot be executed as either pre or post-triggers.
User-defined functions in Azure Cosmos DB are best suited for:
- a) Complex business logic
- b) Calculations
- c) CRUD operations
- d) Data Validation
Answer: b) Calculations
Explanation: User-defined functions are best suited for calculations and computations as they are read-only and have limitations on the operations they can perform.
In Azure Cosmos DB, user-defined functions (UDFs) have ______________
- a) Transactional scope
- b) Global scope
- c) Limited scope
- d) No scope
Answer: a) Transactional scope
Explanation: In Azure Cosmos DB, user-defined functions (UDFs) have a transactional scope, so they are executed atomically during a transaction.
In Azure Cosmos DB, multiple user-defined functions (UDFs) can share a/an _____________
- a) Collection
- b) Scope
- c) Database
- d) Container
Answer: d) Container
Explanation: User-defined functions (UDFs) in Azure Cosmos DB are in a container scope and multiple UDFs can share the same container.
True or False: Azure Cosmos DB UDFs support aggregation functions like MAX/MIN/COUNT etc.
- True
- False
Answer: False
Explanation: Azure Cosmos DB UDFs doesn’t support JavaScript aggregation functions like MAX/MIN/COUNT etc.
In Azure Cosmos DB, User-defined functions are registered and managed through which portal?
- a) Azure portal
- b) Cosmos DB SDK
- c) Azure function app
- d) Both a) Azure portal and b) Cosmos DB SDK
Answer: d) Both a) Azure portal and b) Cosmos DB SDK
Explanation: In Azure Cosmos DB, UDFs are registered and can be managed using either the Azure portal or the Cosmos DB SDK.
True or False: The implementation of a user-defined function in Azure Cosmos DB can be changed without dropping the function.
- True
- False
Answer: True
Explanation: Azure Cosmos DB supports replacing a user-defined function with a new function without needing to drop the function first.
Interview Questions
What is a user-defined function (UDF) in Microsoft Azure Cosmos DB?
A user-defined function (UDF) in Cosmos DB is a piece of JavaScript that is registered for use within queries. They are used to carry out tasks that can’t be achieved by the built-in SQL language such as complex computations, conversions, and string manipulation tasks.
How can you create a UDF in Cosmos DB?
A UDF can be created in Cosmos DB through the Azure portal, or programmatically by using SDKs provided by Cosmos DB.
How are UDFs executed in Cosmos DB?
UDFs in Cosmos DB are executed on the server-side during query execution. They can be used in the SELECT, WHERE, and ORDER BY clauses of a query.
Can a UDF in Cosmos DB modify the data?
No, UDFs in Cosmos DB cannot modify data. They can only perform read-only operations.
How are error handling situations managed, if there is an error within a UDF?
If a UDF results in an error, the entire transaction is rolled back. Therefore, it is set within the Atomicity property of the ACID model.
What is the primary difference between stored procedures and UDFs in Cosmos DB?
The primary difference between stored procedures and UDFs in Cosmos DB is that stored procedures can perform create, read, update, delete (CRUD) operations, while UDFs only perform read operations.
What type of operations can be written in a UDF?
UDFs can perform operations related to mathematical calculations, string manipulations, format conversions, and complex business logic, among others.
Can the execution of a UDF in Cosmos DB affect the Request Unit (RU) charges?
Yes, the execution of a UDF consumes Request Units (RUs), and thus affects the RU charges. The complexity and computational load of the UDF can significantly impact the RU charges.
How do you invoke a UDF within a query in Cosmos DB?
A UDF can be invoked within a query by using its name, like any built-in function. For example, if you have a UDF named “myFunction”, you can use it within a query as: “SELECT value udf.myFunction(c.property) FROM c”.
What language do you use to write a UDF for an Azure Cosmos DB?
A UDF for an Azure Cosmos DB is written in JavaScript.
What are the potential performance impacts of using UDFs in your Cosmos DB queries?
Using UDFs can have potential performance impacts, depending on the complexity and computational load of the UDF. They consume RUs, and if a UDF is doing a complex computation, it can result in increased charge in terms of RUs and can also result in increased latency.
Can UDFs in Cosmos DB accept parameters or arguments?
Yes, UDFs in Cosmos DB can accept parameters or arguments which can be passed when the UDF is invoked in a query.
Can you use UDFs in Cosmos DB outside the scope of a single partition?
No, UDFs in Cosmos DB work within the scope of a single partition, they are not able to span partitions.
What can we return in UDFs in Azure Cosmos DB?
UDFs in Azure Cosmos DB can return any valid JSON compatible value including strings, numbers, booleans, null, arrays, and embedded JSON objects.
Is there a limit on the size of the script for user-defined functions (UDFs) in Cosmos DB?
Yes, the size of the script for UDFs cannot exceed 16 KB.
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