EF Core JSON Column — Complete Guide

In this tutorial, you'll learn about EF Core JSON Column. We cover key concepts, practical examples, and best practices.

You need to store a flexible set of attributes on an entity. You create dozens of nullable columns or a separate key-value table.

Wrong

public class Product
{
    public int Id { get; set; }
    public string? Color { get; set; }
    public string? Size { get; set; }
    public string? Material { get; set; }
    public string? Weight { get; set; }
    // ... more nullable columns for every possible attribute
}

Right

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public Dictionary<string, object> Attributes { get; set; } = new();
}

// Configuration with EF Core 8+
builder.Entity<Product>(b =>
{
    b.OwnsOne(e => e.Attributes)
     .ToJson();
});

// Query JSON properties
var redProducts = await ctx.Products
    .Where(p => p.Attributes["Color"] == "Red")
    .ToListAsync();

Prevention

• Use .ToJson() on owned entities or primitive collections for JSON columns.
• Available in EF Core 8+ for SQL Server, PostgreSQL, and SQLite.
• JSON columns can store complex nested objects and arrays.
• Query JSON properties using standard LINQ.
• Add database indexes on JSON expressions for performance.

Common Mistakes with core json column

1. Using head and tail instead of pattern matching, causing runtime errors on empty lists
2. Forgetting that lazy evaluation defers computation until the value is forced, causing space leaks with unevaluated thunks
3. Using return to exit a function early instead of wrapping a pure value in the monad

These mistakes appear frequently in real-world EF code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ

Which databases support JSON columns in EF Core?

For more EF Core patterns, visit DodaTech.