Searching for entries with empty field (#12376)

* Searching for entries with empty field

* Simplify condition

Author: LoayGhreeb

src/main/java/org/jabref/logic/search/query/SearchToSqlVisitor.java

@@ -207,6 +207,16 @@ public SqlQueryNode visitComparison(SearchParser.ComparisonContext ctx) {
             setFlags(searchFlags, REGULAR_EXPRESSION, true, true);
         }
 
+        // field = "" -> should find entries where the field is empty
+        // field != "" -> should find entries where the field is not empty
+        if (term.isEmpty()) {
+            if (searchFlags.contains(NEGATION)) {
+                searchFlags.remove(NEGATION);
+            } else {
+                searchFlags.add(NEGATION);
+            }
+        }
+
         return getFieldQueryNode(field.toLowerCase(Locale.ROOT), term, searchFlags);
     }
 

src/test/java/org/jabref/logic/search/query/SearchQuerySQLConversionTest.java

@@ -695,6 +695,38 @@ cte0 AS (
                             )
                         )
                         SELECT * FROM cte0 GROUP BY entryid"""
+                ),
+
+                Arguments.of(
+                        "file = \"\"",
+                        """
+                        WITH
+                        cte0 AS (
+                            SELECT main_table.entryid
+                            FROM bib_fields."tableName" AS main_table
+                            WHERE main_table.entryid NOT IN (
+                                SELECT inner_table.entryid
+                                FROM bib_fields."tableName" AS inner_table
+                                WHERE (
+                                    (inner_table.field_name = 'file') AND ((inner_table.field_value_literal ILIKE ('%%')) OR (inner_table.field_value_transformed ILIKE ('%%')))
+                                )
+                            )
+                        )
+                        SELECT * FROM cte0 GROUP BY entryid"""
+                ),
+
+                Arguments.of(
+                        "file != \"\"",
+                        """
+                        WITH
+                        cte0 AS (
+                            SELECT main_table.entryid
+                            FROM bib_fields."tableName" AS main_table
+                            WHERE (
+                                (main_table.field_name = 'file') AND ((main_table.field_value_literal ILIKE ('%%')) OR (main_table.field_value_transformed ILIKE ('%%')))
+                            )
+                        )
+                        SELECT * FROM cte0 GROUP BY entryid"""
                 )
         );
     }