Architecting your own Provider

Want to create a custom search engine that users can query via LINQ? You need to implement IQueryProvider and IQueryable<T>.

1. The Role of the Provider

When a user writes mySource.Where(x => x.Active), your provider receives an Expression Tree. Your job is to visit that tree, understand what the user wants, and translate it into a call to your backend engine (e.g., an Elasticsearch query or a proprietary binary search).

2. The ExpressionVisitor

This is the 'Heart' of any provider. You inherit from ExpressionVisitor to walk through the tree node-by-node. This is a complex 'Expert-Level' task that effectively allows you to extend the C# compiler's power to your own systems.

3. Architect Insight

Q: "Is it worth building a custom provider?"

Architect Answer: "Only if you want to provide a **World-Class Developer Experience (DX)** for your team or customers. Companies like Stripe or MongoDB build these so that developers can use standard C# syntax to query their proprietary APIs. If it's just for an internal project, it's usually overkill—a simple helper method or an OData layer is much faster to build."