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Learn how to address the challenges of querying JSON serialized objects in `EF Core 3.1` and improve your database interactions.
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Understanding the Issue with EF Core 3.1 Querying on JSON Serialized Objects

When working with Entity Framework Core (EF Core) and its ability to serialize collections into JSON format, developers may run into some unexpected issues, especially when trying to execute queries on those JSON serialized fields. If you've encountered the frustrating situation where you cannot query against a JSON serialized list in EF Core, you're not alone. This guide dives deep into the underlying problems and presents solutions that can help developers navigate these challenges.

The Problem at Hand

Let's consider the following model where we store related video IDs as JSON serialized data:

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

In your EF Core context configuration, you serialize the IList<int> property AllRelatedIds to a JSON string. Everything works seamlessly when adding, editing, or deleting items:

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

However, problems arise when attempting to execute queries such as:

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

To your dismay, the result is null, even if the related IDs contain the value you're looking for. Furthermore, when trying to count how many videos contain the related ID, you encounter errors indicating that the query could not be translated.

Why Does This Happen?

The root of the issue lies in how EF Core handles JSON serialization and deserialization. Here are the key points to understand:

Application-Level Serialization: EF Core serializes the IList<int> into a single string value (e.g., [11000,12000,13000]) before sending it to the database. Similarly, it deserializes this string back into an IList<int> after fetching the data from the database.

Single Data Entity: To the database, the JSON representation is a single data entity, not a collection. As a result, the database cannot perform operations on collections when they are stored as JSON strings.

Query Translation Failure: When you write a query such as t.AllRelatedIds.Contains(11000), EF Core attempts to translate this into SQL, which fails because the database does not understand how to handle collections in a JSON format.

How to Solve the Issue

Although it seems inefficient to retrieve all video records just to apply a filter, it opens up some potential workarounds. Below are a couple of ways you can work with this limitation:

Option 1: Fetch All Records

One straightforward option is to retrieve all records and then apply your filtering on the client-side:

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

Option 2: Redesign Database Structure

While the first option is a quick fix, it's important to recognize that it may not be the most performant solution. Ideally, a better design would involve normalizing your data structure:

Create a Related Table: Instead of relying on JSON strings to store collections, consider using a separate table to manage related IDs. This design will allow you to run queries against related data efficiently.

Final Thoughts

Encountering issues with querying JSON serialized objects in EF Core 3.1 can be frustrating, but understanding the problem helps you determine the best course of action. While fetching all records may suffice in the short term, evaluating your database structure can yield more efficient, long-lasting solutions.

As you work with EF Core, keep these principles in mind to optimize your queries and prevent similar issues in the future.