Fix IndexOf

src/EFCore.Jet/Query/ExpressionTranslators/Internal/JetStringMethodTranslator.cs

@@ -308,29 +308,31 @@ namespace EntityFrameworkCore.Jet.Query.ExpressionTranslators.Internal
                 argumentsPropagateNullability,
                 method.ReturnType);
 
-            charIndexExpression = _sqlExpressionFactory.Subtract(charIndexExpression, _sqlExpressionFactory.Constant(1));
-
             // If the pattern is an empty string, we need to special case to always return 0 (since CHARINDEX return 0, which we'd subtract to
             // -1). Handle separately for constant and non-constant patterns.
-            if (searchExpression is SqlConstantExpression { Value: string constantSearchPattern })
+            if (searchExpression is SqlConstantExpression { Value: "" })
             {
-                return constantSearchPattern == string.Empty
-                    ? _sqlExpressionFactory.Constant(0, typeof(int))
-                    : charIndexExpression;
+                return _sqlExpressionFactory.Case(
+                    [new(_sqlExpressionFactory.IsNotNull(instance), _sqlExpressionFactory.Constant(0))],
+                    elseResult: null
+                );
             }
 
-            return _sqlExpressionFactory.Case(
-                new[]
-                {
-                new CaseWhenClause(
-                    _sqlExpressionFactory.Equal(
-                        searchExpression,
-                        _sqlExpressionFactory.Constant(string.Empty, stringTypeMapping)),
-                    _sqlExpressionFactory.Constant(0))
-                },
-                charIndexExpression);
-        }
+            SqlExpression offsetExpression = searchExpression is SqlConstantExpression
+                ? _sqlExpressionFactory.Constant(1)
+                : _sqlExpressionFactory.Case(
+                    new[]
+                    {
+                        new CaseWhenClause(
+                            _sqlExpressionFactory.Equal(
+                                searchExpression,
+                                _sqlExpressionFactory.Constant(string.Empty, stringTypeMapping)),
+                            _sqlExpressionFactory.Constant(0))
+                    },
+                    _sqlExpressionFactory.Constant(1));
 
 
+            return _sqlExpressionFactory.Subtract(charIndexExpression, offsetExpression);
+        }
     }
 }