Migration to 5.0

The new JSQLParser 5 introduces API-breaking changes:

1. Dependency on Java 11 or newer

2. Reworked AST Visitors

   The AST Visitors have been reworked to pass a Generic Context from the Root Node down to the Leaves.

   Generic Interface

   public interface SelectVisitor<T> {
   
       <S> T visit(PlainSelect plainSelect, S context);
   
       default void visit(PlainSelect plainSelect) {
           this.visit(plainSelect, null);
       }
   
   }
   

   Sample Implementation

   public class JSQLColumnResolver
       implements SelectVisitor<JdbcResultSetMetaData>, FromItemVisitor<JdbcResultSetMetaData> {
   
       @Override
       public <S> JdbcResultSetMetaData visit(PlainSelect select, S context) {
           if (context instanceof JdbcMetaData) {
               return visit(select, (JdbcMetaData) context);
           }
           return null;
       }
   
       public JdbcResultSetMetaData visit(PlainSelect select, JdbcMetaData metaData) {
           JdbcResultSetMetaData resultSetMetaData = new JdbcResultSetMetaData();
   
           // Logic to retrieve the column information
           resultSetMetaData = getColumn(metaData, select.getFromItem(), select.getJoins());
   
           return resultSetMetaData;
       }
   }
   

3. Generic Result from Leaves to Root

   Node objects now return a Generic Result from the Leaves up to the Root.

   AST Node

   public class PlainSelect extends Select {
       @Override
       public <T, S> T accept(SelectVisitor<T> selectVisitor, S context) {
           return selectVisitor.visit(this, context);
       }
   }
   

How is this useful? Consider resolving the AllColumns * or AllTableColumns t.* expressions to retrieve the actual column names. This process depends on the database’s physical metadata and the context of the current scope, including virtual data frames (like sub-selects and with-clauses).

Therefore, every branch of the AST must receive scoped metadata from its parent node. Each AST node must receive the resolved columns from its child nodes. A global result object (like the StringBuilder in the DepParser implementations) is inadequate.

Alternatively, consider substituting TimeValueKey (CURRENT_DATE, CURRENT_TIME, etc.) with actual date or time values. You can push a simple Map of key/value pairs down to the Expression Visitor:

Expression Visitor

@Override
public <S> StringBuilder visit(TimeKeyExpression expression, S context) {
    if (context instanceof Map) {
        return visit(expression, (Map<String, Object>) substitutions);
    } else {
      return expression.toString();
    }
}

public StringBuilder visit(TimeKeyExpression expression, Map<String, Object> substitutions) {
    // Remove possible trailing brackets "()"
    String value = expression.getStringValue().toUpperCase().replaceAll("[()]", "");

    if (substitutions.containsKey(value)) {
        // @todo: Cast Date/Time types
        return castDateTime(substitutions.get(value).toString()).accept(this, null);
    } else {
        return super.visit(expression, null);
    }
}

Another advantage is parallel processing: Without relying on a global result object, the AST can be traversed in parallel (whereas it currently must be traversed strictly in serial).

Finally, any child node can now know its parent and identify who called it.