Azure Cosmos DB is a Microsoft-owned, global multi-model database service for managing data at a large scale. As part of the examination for DP-420 Designing and Implementing Native Applications Using Microsoft Azure Cosmos DB, it is crucial to understand how to implement queries that use array and type-checking functions. These sets of skills require a fundamental understanding of various Azure Cosmos DB features and programming structures in use today. Let’s explore these array and type-checking functions illustratively.
Array Functions in Azure Cosmos DB
Array functions in Azure Cosmos DB are essential for complex types. Querying these sophisticated types necessitates knowledge of the Array functions and how to put them into use. Below are some common array functions that can be applied:
Array_Contains: This function checks if the specified array contains a particular element. Use this function to filter for documents where the array contains a particular element.
For instance:
SELECT * FROM c WHERE ARRAY_CONTAINS(c.tags, 'azure')
In the query above, we select all from a collection where the ‘tags’ array includes ‘azure’.
Array_Length: This function returns the number of elements in the array. It can be used to filter for documents where the array contains a specific amount of elements.
A practical example is as follows:
SELECT * FROM c WHERE ARRAY_LENGTH(c.tags) > 2
Type-Checking Functions
Type-checking functions are used to verify the data type of an object. This is pivotal in ensuring data integrity and accuracy during operations. Below are some common type-checking functions available in Azure Cosmos DB.
IS_ARRAY: This function returns true if a specified property is an array.
For instance:
SELECT * FROM c WHERE IS_ARRAY(c.property)
In the query above, it selects all from the collection where ‘property’ is an array.
IS_BOOL: Returns true if a specified property is a boolean.
For example:
SELECT * FROM c WHERE IS_BOOL(c.isComplete)
The query above selects all from the collection where ‘isComplete’ is a boolean.
Other type-checking functions include IS_NULL, IS_DEFINED, IS_NUMBER, IS_OBJECT, and IS_STRING.
Comparison of Array and Type-checking Functions
Array functions and type-checking functions serve different purposes and have different uses. Here is a simple comparison table:
| Category | Purpose | Example |
|---|---|---|
| Array Functions | Array functions are used for managing and interacting with complex types in Azure Cosmos DB. | ARRAY_CONTAINS(c.tags, ‘azure’) |
| Type-Checking Functions | Type-checking functions are used for ensuring data integrity by verifying the datatype of an object or property. | IS_ARRAY(c.property) |
Conclusion
Mastering the implementation of array and type-checking functions in Azure Cosmos DB is a critical aspect of the DP-420 examination. As these functions enable efficient management and interaction with complex types and data integrity checks, building competency around them ensures the creation of powerful, robust applications in the Azure environment.
Practice Test
True or False: In Cosmos DB, you can use the .NET SDK to implement queries that use array and type-checking functions.
- True
- False
Answer: True
Explanation: The .NET SDK in Cosmos DB provides powerful array and type-checking functionalities for implementing queries.
Which of the following statements are correct related to implementing queries using Microsoft Azure Cosmos DB?
- a) Queries can be written using SQL API
- b) Queries can be written only in C#
- c) ARRAY_CONTAINS function is useful for array properties
- d) ARRAY_CONTAINS function can only be used with SQL API
Answer: a), c)
Explanation: In Cosmos DB, queries can be written using SQL API or other provided APIs. The ARRAY_CONTAINS function is important for querying array properties and it can be used across different APIs.
True or False: You cannot use the ARRAY_CONTAINS function in a JOIN clause in Cosmos DB queries.
- True
- False
Answer: False
Explanation: ARRAY_CONTAINS can be used in a JOIN clause in Cosmos DB queries to filter and match documents.
Which of these are valid array functions in Cosmos DB SQL API?
- a) ARRAY_ADD
- b) ARRAY_SELECT
- c) ARRAY_CONCAT
- d) ARRAY_REMOVE
Answer: c)
Explanation: Among the options, ARRAY_CONCAT is a valid array function in the SQL API of Cosmos DB.
What is the purpose of the IS_DEFINED function in Cosmos DB SQL API?
- a) To check if a property exists in a document
- b) To retrieve the value of a property
- c) To delete a property from a document
Answer: a)
Explanation: The IS_DEFINED function is used to check if a specific property exists in a document in Cosmos DB.
True or False: Azure Cosmos DB support operations to add or remove elements from an existing array within a document.
- True
- False
Answer: False
Explanation: Azure Cosmos DB do not support operations to add or remove elements directly from an existing array within a document.
Which of the following functions is used to check the type of a property in Cosmos DB SQL API?
- a) IS_DEFINED
- b) IS_TYPE
- c) TYPEOF
- d) CHECK_TYPE
Answer: c) TYPEOF
Explanation: The TYPEOF function is used to check the type of a property in Cosmos DB SQL API.
True or False: In Cosmos DB, you cannot perform array and type-checking functions using the MongoDB API.
- True
- False
Answer: False
Explanation: Cosmos DB provides MongoDB API which allows implementing array and type-checking functions.
The SQL API in Cosmos DB supports which of the following type-checking functions?
- a) IS_STRING
- b) IS_NUMBER
- c) IS_BOOLEAN
- d) All of the above
Answer: d) All of the above
Explanation: Cosmos DB SQL API supports IS_STRING, IS_NUMBER, and IS_BOOLEAN functions to check the type of a property.
True or False: ARRAY_CONTAINS() function in SQL API is case-insensitive.
- True
- False
Answer: False
Explanation: ARRAY_CONTAINS() function in SQL API is case-sensitive. You must exactly match the case of string values to get expected results.
Which of the following is the correct way to use IS_DEFINED function in Cosmos DB SQL API?
- a) SELECT * FROM c WHERE IS_DEFINED(c.property) = true
- b) SELECT * FROM c IS_DEFINED(c.property)
- c) SELECT * FROM c WHERE IS_DEFINED(c.property)
Answer: a) SELECT * FROM c WHERE IS_DEFINED(c.property) = true
Explanation: IS_DEFINED function is used in Cosmos DB to check if a property is defined or not and it returns a boolean. The correct usage is IS_DEFINED(c.property) = true or false.
Can you use the ‘!=’ operator with IS_DEFINED function in Cosmos DB SQL API?
- a) Yes
- b) No
Answer: b) No
Explanation: The ‘!=’ operator is not supported with IS_DEFINED function in Cosmos DB SQL API. The correct usage is IS_DEFINED(property) = true or false.
True or False: By default, Cosmos DB includes all array elements in query results.
- True
- False
Answer: True
Explanation: By default, Cosmos DB’s SQL API includes all array elements in the result set while using JOINs unless otherwise specified in the query.
Can you check for null values in an array property using ARRAY_CONTAINS function?
- a) Yes
- b) No
Answer: a) Yes
Explanation: The ARRAY_CONTAINS function can be used to check if an array property contains null values in Cosmos DB.
True or False: The TYPEOF function can be used with nested properties.
- True
- False
Answer: True
Explanation: The TYPEOF function can be used with nested properties in Cosmos DB to check the type of a nested property.
Interview Questions
What is the function of Array Contains in Azure Cosmos DB?
The Array Contains function in Azure Cosmos DB checks if the supplied value exists in an array within a document.
How do you check if a property value is of a certain data type in Azure Cosmos DB?
You can use the built-in functions IS_BOOLEAN, IS_STRING, IS_ARRAY etc to check if the value of a property is of a specified data type in Azure Cosmos DB.
What happens when you use the IS_DEFINED function in Azure Cosmos DB?
The IS_DEFINED function in Azure Cosmos DB checks if the property is defined in a document. It returns true if the property is defined and false if it is not.
How can you search an array for a value in Azure Cosmos DB?
You can use the ARRAY_CONTAINS built-in function to search an array for a value in Azure Cosmos DB. The function returns true if the value is found and false otherwise.
Can the IS_NULL function be used with array type in Azure Cosmos DB?
Yes, the IS_NULL function can be used with array type in Azure Cosmos DB to check if the value of an array is null.
What are type checking functions in Azure Cosmos DB?
Type checking functions in Azure Cosmos DB are built-in methods that allow you to check the datatype of a property value in a document.
What is the purpose of IS_NUMBER function in Cosmos DB?
The IS_NUMBER function is used to check if a property value in a document is of numeric type in Microsoft Azure Cosmos DB.
How can you verify if a property exists in a document or not in Azure Cosmos DB?
In Azure Cosmos DB, you can use the IS_DEFINED function to verify if a property exists in a document or not.
How do you know whether a particular value is a string or not in Azure Cosmos DB?
In Azure Cosmos DB, you can use the IS_STRING function to verify whether a particular value is a string or not.
How can the ARRAY_LENGTH function be used in Azure Cosmos DB?
The ARRAY_LENGTH function in Azure Cosmos DB is used to retrieve the number of elements in an array.
What will be the return value of IS_NULL function in Cosmos DB if applied to an undefined property?
If the IS_NULL function in Cosmos DB is applied to an undefined property, it will return true.
Can IS_DEFINED function be used to check null values?
No, IS_DEFINED function can not be used to check null values in Cosmos DB. However, it can be used to check if a property exists in a document or not.
What is the purpose of the IS_PRIMITIVE function in Cosmos DB?
The IS_PRIMITIVE function in Cosmos DB is used to check if a value is of a primitive datatype (string, number, Boolean or null) or not.
Is it possible to nest ARRAY_CONTAINS function inside another ARRAY_CONTAINS function in Cosmos DB?
Yes, it is possible to nest ARRAY_CONTAINS function inside another ARRAY_CONTAINS function in Cosmos DB for a more complex search.
What will be the return value of IS_PRIMITIVE function in Cosmos DB if applied on a non-primitive data type like an array?
If the IS_PRIMITIVE function in Cosmos DB is applied to a non-primitive data type like an array, it will return false.
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