How to Resolve 'Unable to Update EntitySet Due to DefiningQuery and Missing UpdateFunction' in Entity Framework 1?

TypeError: Unable to Update EntitySet Due to DefiningQuery and Missing UpdateFunction

In Entity Framework 1 with .NET 3.5, an error may occur when attempting to update an entity:

Unable to update the EntitySet - because it has a DefiningQuery and no <UpdateFunction> element exists in the <ModificationFunctionMapping> element to support the current operation.

This error originates from one of the following scenarios:

• The entity set is mapped from a database view.
• A custom database query is being used.
• The database table corresponding to the entity lacks a primary key.

It's essential to verify that a primary key is defined for the entity, even if it seems apparent at first glance. To resolve the issue:

1. Ensure that the entity is mapped to a table with a primary key in the database.
2. Open the Entity Framework designer and update the mapping (or manually remove and then re-add the entity).

Following these steps will typically eliminate the "Unable to update the EntitySet" error and allow updates to be executed successfully.

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