Скачать или смотреть How to Add Missing Struct Items to an Array in GRDB without Causing Errors

Learn how to work around the issue of adding missing struct items in GRDB when fetching from your database, ensuring your Swift app runs smoothly.
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This video is based on the question https://stackoverflow.com/q/66861641/ asked by the user 'Quailcreek' ( https://stackoverflow.com/u/11004336/ ) and on the answer https://stackoverflow.com/a/66866649/ provided by the user 'Gwendal Roué' ( https://stackoverflow.com/u/525656/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving Missing Struct Items in GRDB: A Guide for Swift Developers

When working with databases in iOS applications using GRDB, developers often encounter challenging scenarios. One such situation arises when you need to fetch data that lacks certain struct properties, causing runtime errors. This guide will guide you through a solution for adding items to an array in Swift that are defined in a struct but not present in the database table, ensuring your app functions seamlessly.

Understanding the Issue

Imagine you have a table named My_Quotes in your database, from which you pull contact information to construct a QuoteList struct. The challenge here is that while you pull a valid ContactID, the ContactFullName, ContactFirst, ContactLast, and ContactOrg values are not stored in that table. This mismatch will lead to a Fatal error: could not read String from missing column ContactFullName when you attempt to access these properties.

The Root Cause

The underlying problem stems from assigning the QuoteList struct the FetchableRecord protocol, which expects to map all necessary data from the database into its properties. Since the My_Quotes table doesn't contain information for the aforementioned contact properties, GRDB cannot instantiate QuoteList properly.

Solutions to the Problem

To resolve this issue, consider the following alternative methods that allow you to fetch the required data without error:

Option 1: Fetch Raw Database Rows

Instead of fetching directly into your QuoteList, fetch raw rows from the database. This approach allows you to manually construct QuoteList items with the required contact details. The modified code could look like this:

[[See Video to Reveal this Text or Code Snippet]]

Option 2: Define a Fetchable Model for Partial Data

If you still want to leverage the FetchableRecord capabilities of GRDB, create a separate model that represents only the properties present in the My_Quotes table:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By using the outlined strategies, you can effectively handle scenarios where your structs require additional information not represented in the database. This will not only mitigate errors but also keep your application robust and user-friendly. Writing clean, maintainable code while manipulating database records is key in making your Swift development experience a productive one.

Using GRDB efficiently is about understanding the data model and handling discrepancies wisely. Whenever you find that your app's structure doesn't align with data retrieval expectations, consider employing these techniques to maintain functionality and ensure user satisfaction.