Robust Data Updates with TRY/CATCH

In database operations, errors are inevitable, ranging from invalid data inputs to constraint violations. Gracefully handling these errors is crucial for maintaining data integrity and ensuring the smooth operation of applications. This challenge focuses on implementing robust data update procedures using TRY/CATCH blocks in SQL-like pseudocode to manage potential exceptions.

Problem Description

You are tasked with creating a stored procedure or function that attempts to update records in a Products table. The update operation should be enclosed within a TRY block. If any error occurs during the update (e.g., a constraint violation, division by zero, invalid data type), the CATCH block should be executed. The CATCH block must log the error details into an ErrorLog table and then rollback any changes made within the TRY block to ensure data consistency.

Key Requirements:

• Atomic Operation: The entire update process for a single product should be treated as an atomic unit. Either all changes are committed, or none are.
• Error Logging: When an error occurs, specific details about the error must be captured.
• Rollback: If an error occurs, all modifications made within the TRY block must be undone.
• Success Indication: The procedure should provide a way to indicate whether the operation was successful or not.

Expected Behavior:

• If the update operation in the TRY block completes without any errors, the changes should be committed, and the procedure should indicate success.
• If any error occurs within the TRY block, the CATCH block should execute, logging the error and rolling back the transaction. The procedure should then indicate failure.

Edge Cases:

• Multiple Errors: Consider how the CATCH block handles situations where multiple potential errors could occur within a single TRY block. The CATCH block should handle the first encountered error.
• Zero-Value Operations: Operations that might lead to division by zero or other arithmetic errors.
• Data Type Mismatches: Attempts to insert or update data with incorrect data types.

Examples

Example 1:

Input:
  - ProductID: 101
  - NewPrice: 50.00
  - NewStock: 100

Operation in TRY block:
  UPDATE Products
  SET Price = NewPrice, Stock = NewStock
  WHERE ProductID = ProductID;

Expected Output (Success):
  - Message: "Product update successful."
  - Products table for ProductID 101: Price = 50.00, Stock = 100
  - ErrorLog table: Empty

Explanation:
  The update operation for ProductID 101 is valid and completes without errors. The transaction is committed.

Example 2:

Input:
  - ProductID: 102
  - NewPrice: -10.00 (Invalid price)
  - NewStock: 50

Operation in TRY block:
  UPDATE Products
  SET Price = NewPrice, Stock = NewStock
  WHERE ProductID = ProductID;

Expected Output (Failure):
  - Message: "Product update failed. See error log for details."
  - Products table for ProductID 102: Price and Stock remain unchanged from their original values.
  - ErrorLog table: Contains a record with details of the invalid price constraint violation.

Explanation:
  The `NewPrice` of -10.00 violates a `CHECK` constraint (e.g., Price >= 0). The `TRY` block encounters this error. The `CATCH` block logs the error, and the transaction is rolled back, leaving ProductID 102's data unchanged.

Example 3:

Input:
  - ProductID: 103
  - NewPrice: 75.00
  - NewStock: 200

Operation in TRY block:
  DECLARE @InvalidValue INT;
  SET @InvalidValue = 10 / 0; -- This will cause a division by zero error
  UPDATE Products
  SET Price = NewPrice, Stock = NewStock
  WHERE ProductID = ProductID;

Expected Output (Failure):
  - Message: "Product update failed. See error log for details."
  - Products table for ProductID 103: Price and Stock remain unchanged.
  - ErrorLog table: Contains a record with details of the division by zero error.

Explanation:
  The `TRY` block attempts a division by zero operation before the update. This error is caught by the `CATCH` block. The error is logged, and the entire transaction, including any potential partial updates (though none occurred before the error in this specific case), is rolled back.

Constraints

• The Products table has columns ProductID (integer, primary key), Price (decimal, cannot be negative), and Stock (integer, cannot be negative).
• The ErrorLog table has columns ErrorID (auto-incrementing integer, primary key), ErrorMessage (text), ErrorSeverity (integer), ErrorState (integer), ErrorTimestamp (datetime).
• The stored procedure/function should accept ProductID, NewPrice, and NewStock as input parameters.
• The response should indicate success or failure via a status message or return value.
• The entire TRY/CATCH block should execute within a single transaction.

Notes

• The specific syntax for TRY/CATCH blocks and transaction management (e.g., BEGIN TRANSACTION, COMMIT TRANSACTION, ROLLBACK TRANSACTION) may vary slightly between different SQL dialects, but the pseudocode should represent the general concept.
• Consider how to retrieve error details within the CATCH block. Many SQL systems provide built-in functions for this purpose (e.g., ERROR_MESSAGE(), ERROR_SEVERITY(), ERROR_STATE() in T-SQL).
• The pseudocode should clearly delineate the TRY and CATCH sections and demonstrate the transactional control flow.