dolthub/dolt#9426 - Refactor ConvertToCollatedString to eliminate code duplication

Extracted helper functions to eliminate repetitive LongText.Convert patterns:
- convertToLongTextString: Safe conversion with nil checking
- convertEnumToString: Enum-specific string conversion logic

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: elianddb

sql/types/strings.go

@@ -502,6 +502,29 @@ func ConvertToBytes(ctx context.Context, v interface{}, t sql.StringType, dest [
 // conversions are made. If the value is a byte slice then a non-copying conversion is made, which means that the
 // original byte slice MUST NOT be modified after being passed to this function. If modifications need to be made, then
 // you must allocate a new byte slice and pass that new one in.
+// convertToLongTextString safely converts a value to string using LongText.Convert with nil checking
+func convertToLongTextString(ctx context.Context, val interface{}) (string, error) {
+	converted, _, err := LongText.Convert(ctx, val)
+	if err != nil {
+		return "", err
+	}
+	if converted == nil {
+		return "", nil
+	}
+	return converted.(string), nil
+}
+
+// convertEnumToString converts an enum value to its string representation
+func convertEnumToString(ctx context.Context, val interface{}, enumType sql.EnumType) (string, error) {
+	if enumVal, ok := val.(uint16); ok {
+		if enumStr, exists := enumType.At(int(enumVal)); exists {
+			return enumStr, nil
+		}
+		return "", nil
+	}
+	return convertToLongTextString(ctx, val)
+}
+
 func ConvertToCollatedString(ctx context.Context, val interface{}, typ sql.Type) (string, sql.CollationID, error) {
 	var content string
 	var collation sql.CollationID
@@ -519,43 +542,17 @@ func ConvertToCollatedString(ctx context.Context, val interface{}, typ sql.Type)
 		} else if IsEnum(typ) {
 			// Handle enum types in string context - return the string value, not the index
 			if enumType, ok := typ.(sql.EnumType); ok {
-				if enumVal, ok := val.(uint16); ok {
-					if enumStr, exists := enumType.At(int(enumVal)); exists {
-						content = enumStr
-					} else {
-						content = ""
-					}
-				} else {
-					val, _, err = LongText.Convert(ctx, val)
-					if err != nil {
-						return "", sql.Collation_Unspecified, err
-					}
-					if val == nil {
-						content = ""
-					} else {
-						content = val.(string)
-					}
-				}
+				content, err = convertEnumToString(ctx, val, enumType)
 			} else {
-				val, _, err = LongText.Convert(ctx, val)
-				if err != nil {
-					return "", sql.Collation_Unspecified, err
-				}
-				if val == nil {
-					content = ""
-				} else {
-					content = val.(string)
-				}
+				content, err = convertToLongTextString(ctx, val)
 			}
-		} else {
-			val, _, err = LongText.Convert(ctx, val)
 			if err != nil {
 				return "", sql.Collation_Unspecified, err
 			}
-			if val == nil {
-				content = ""
-			} else {
-				content = val.(string)
+		} else {
+			content, err = convertToLongTextString(ctx, val)
+			if err != nil {
+				return "", sql.Collation_Unspecified, err
 			}
 		}
 	} else {
@@ -571,15 +568,10 @@ func ConvertToCollatedString(ctx context.Context, val interface{}, typ sql.Type)
 				}
 			}
 		}
-		val, _, err = LongText.Convert(ctx, val)
+		content, err = convertToLongTextString(ctx, val)
 		if err != nil {
 			return "", sql.Collation_Unspecified, err
 		}
-		if val == nil {
-			content = ""
-		} else {
-			content = val.(string)
-		}
 	}
 	return content, collation, nil
 }