Beyond LIKE: Efficient Full Text Search Strategies in LINQ

LINQ translates its operations into standard SQL queries, which might not directly map to FTS functionalities like the CONTAINS operator. Instead, LINQ often utilizes the regular LIKE operator, which doesn't leverage FTS indexes, resulting in potentially slower and less efficient searches.

Example:

Imagine you want to search for documents containing "report" and "sales" using LINQ.

var documents = context.Documents
    .Where(d => d.Content.Contains("report") && d.Content.Contains("sales"));

This translates to:

SELECT * FROM Documents
WHERE Content LIKE '%report%' AND Content LIKE '%sales%';

While this query retrieves documents with both terms, it won't benefit from FTS indexes and might perform full table scans, impacting performance.

Solutions:

Here are two approaches to integrate FTS with LINQ:

Using a User-Defined Function (UDF):

1. Create a UDF in SQL Server that accepts search terms and utilizes CONTAINSTABLE to perform FTS.
2. Map this UDF to your LINQ model, allowing you to call it within your query.

// UDF in SQL Server (fts_Search)
CREATE FUNCTION fts_Search(@terms nvarchar(4000))
RETURNS TABLE
AS
RETURN (
  SELECT DocumentId, RANK() OVER (ORDER BY (SELECT NULL)) AS Rank
  FROM CONTAINSTABLE(Documents, (Content), @terms)
);

// LINQ query
var documents = context.Documents
    .Join(context.fts_Search(searchTerm), d => d.Id, f => f.DocumentId, (d, f) => d);

This approach enables leveraging FTS within LINQ but requires additional SQL Server coding and model mapping.

Utilizing Entity Framework Core Interceptors:

1. Implement a custom interceptor for Entity Framework Core that intercepts queries containing specific keywords and rewrites them to utilize FTS functions like CONTAINS.
2. This interceptor modifies the generated SQL, enabling FTS functionality within LINQ queries.

This method offers a more dynamic solution but might require deeper understanding of Entity Framework Core internals and custom code development.

Important Note:

Both solutions involve workarounds and have their own complexities. It's essential to evaluate the trade-offs based on your specific needs and expertise.

Additional Considerations:

• Ensure you have FTS properly configured and enabled in your SQL Server instance.
• Understand the limitations and potential performance implications of each approach.
• Consider alternative full-text search solutions outside of SQL Server FTS, depending on your specific requirements.