Check if a Record Already Exists in the Database Using Delphi

Discover how to effectively check the existence of records in a Firebird Database using Delphi RIO 10.3 and Firedac components.
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This video is based on the question https://stackoverflow.com/q/63054193/ asked by the user 'Ederson Silva' ( https://stackoverflow.com/u/6714492/ ) and on the answer https://stackoverflow.com/a/63055391/ provided by the user 'MartynA' ( https://stackoverflow.com/u/2663863/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Checking If a Record Already Exists in the Database using Delphi

When working with databases in Delphi, a common challenge developers face is verifying whether a certain record exists in your database before performing actions such as drawing or displaying data. In this article, we will address a scenario involving a cxGrid and provide a structured solution to check for records in a Firebird database using Delphi RIO 10.3 and firedac components.

The Problem

A developer encountered an issue where they needed to compare products displayed in a cxGrid with those already registered in the database. They wanted to change the color of the grid cell based on whether a product exists in the database. The initial approach involved working within the cxGridProdutoCustomDrawCell event but it didn't yield the desired results. The primary challenge was determining if the comparison logic was functioning correctly.

Here’s the key snippet of the existing code:

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Steps to Identify and Solve the Issue

To resolve the issue, we need to follow a systematic approach, which involves testing the color changes independently and ensuring the data comparison is valid. Here’s how you can do it:

Step 1: Test Text Color

First, we need to ensure that the font color changes correctly. Modify the code in the cxGridProdutoCustomDrawCell event to force the font color to red:

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Run your application to confirm that the text in the cell is indeed red. If the text doesn't appear as red, there may be a different issue that you need to diagnose first.

Step 2: Validate the Comparison Logic

Once you confirm that the font color changes correctly, return to your original code. Add variables to store the retrieved values from your queries for clarity and debugging convenience:

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After implementing this modification, set a breakpoint on the line containing the comparison. While running the application, when the execution hits the breakpoint, check the values of S1 and S2. You are looking to determine whether these are continuously equal or not, as the problem may lie in the datasource or logic feeding these values.

Step 3: Ensure Proper Synchronization of Queries

Another critical aspect to consider is which query is tied to the grid view and which query is used for comparisons. Before checking the values, you should ensure that the other query is properly synchronized. To confirm if a specific product exists in your dataset, it’s recommended to utilize a locate function as follows:

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Utilizing the Locate method allows you to ensure that the value from the grid is accurately represented in the other query, providing a reliable way to check record existence.

Conclusion

In summary, checking if a record exists in a database using Delphi requires a systematic approach to ensure the logic is functioning as intended. By validating font color changes, refining comparison logic, and ensuring query synchronization, you can effectively manage how records are displayed and how they correspond to your database.

This step-by-step guide is designed to enhance your understanding and application of Delphi with Firebird databases, leading to more robust applications.