Скачать или смотреть Solving the Microsoft Sync Framework Unique Index Error in SQL Server and SQL CE

Discover how to fix the unique index error in the Microsoft Sync Framework when syncing SQL Server with SQL CE databases, optimizing GUID keys and multi-column constraints for improved data handling.
---
This video is based on the question https://stackoverflow.com/q/64401470/ asked by the user 'juergen d' ( https://stackoverflow.com/u/575376/ ) and on the answer https://stackoverflow.com/a/64438490/ provided by the user 'seanb' ( https://stackoverflow.com/u/14267425/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Microsoft Sync Framework unique index error

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Resolving the Microsoft Sync Framework Unique Index Error

The Microsoft Sync Framework is a powerful tool for synchronizing databases, allowing applications to operate offline seamlessly. However, users sometimes encounter issues, such as the unique index error, when trying to sync data between SQL Server and a local SQL CE database. This guide will explore the root cause of this error and provide a comprehensive solution to effectively manage synchronizations that involve unique index constraints.

Understanding the Problem

When synchronizing your SQL Server instance with a local SQL CE file, you might define a unique index to ensure data integrity. In this case, the structure of your usersettings table includes a composite unique index based on two columns: user_id and setting_id. An example of the table structure could look like this:

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

During a sync operation, when you create records with the same user_id and setting_id in both databases, you're likely to encounter an error message indicating that a duplicate value cannot be inserted into a unique index. This issue arises because each database assigns its own unique IDs (GUIDs) for the id column, leading to conflicting primary keys.

Why Does the Error Occur?

The core of the problem lies in the handling of keys during synchronization:

When you create new records in both databases, they may contain identical values for the user_id and setting_id but distinct primary key values in the id column.

This variance generates a conflict when trying to sync, as the Synchronization Framework does not simply update the record; it attempts to insert a new one with a duplicate key, violating the unique constraint.

Steps to Solve the Unique Index Error

To avoid this unique index issue while still retaining the ability to sync data correctly, consider the following adjustments to your usersettings table structure:

1. Remove the Redundant Primary Key

Since the usersettings table acts as a many-to-many relationship between users and settings, the individual id primary key may be unnecessary. Instead, define a composite primary key using the existing foreign keys:

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

This change will make the combination of user_id and setting_id the primary key, reducing the chance of conflict during synchronization.

2. Maintain Proper Field Types

Ensure that the data types of your foreign keys are consistent across both databases. This consistency helps avoid errors and ensures smoother merges during synchronization.

3. Consider Concatenating Keys as a Unique Identifier

If having a single column as a unique identifier is essential for your design, an alternative is to concatenate the user_id and setting_id to generate a readable primary key (e.g., a VARCHAR that incorporates both IDs). Here’s how you can implement it:

Convert the composite keys into a unique string as primary key:

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

Populate the primary key with the concatenated values:

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

Conclusion

Handling unique index errors in the Microsoft Sync Framework requires strategic planning of your database schema. By adjusting your table structure to remove unnecessary primary keys, maintaining proper data types, and, if needed, generating a meaningful unique identifier, you can resolve synchronization conflicts effectively. Remember, the goal is to simplify the data model to allow for seamless merging of identical entries.

With these strategies in place, your experience with the Microsoft Sync Framework will be much smoother, enabling efficient offline work wi