DBLinq.Firebird中Single()与SingleOrDefault实现异常的技术咨询

I ran into a significant issue with the SingleOrDefault method in the DBLinq.Firebird/FirebirdSql.Data.FirebirdClient provider, and wanted to break down the problem clearly:

The Problem #

When querying a table that has multiple records matching the filter (for example, multiple rows where CD = 5), executing this LINQ query:

dbContext.GetTable<TABLE>().SingleOrDefault(r => r.CD == 5)

does not throw an exception as it should.

Expected vs. Actual Behavior #

• Expected: Per standard LINQ contract, SingleOrDefault should throw an InvalidOperationException when more than one matching record exists — this method is designed for scenarios where you expect 0 or exactly 1 result.
• Actual: The method returns the first matching record without any error, completely ignoring the presence of additional matching rows.

Root Cause #

Digging into the underlying SQL generated by the provider reveals the core issue:

SELECT FIRST 2 * FROM TABLE WHERE (CD == @CD)

The provider correctly fetches up to 2 records (a standard approach to detect multiple matches), but the SingleOrDefault implementation fails to validate if the result set contains 2 records. It simply returns the first record instead of triggering the expected exception.

内容的提问来源于stack exchange，提问作者MariusB