Java 用于获取WHERE子句的FoundationDB SQL解析器

我正在使用foundationDB SQL解析器（）在Java内部解析查询，但我对解析器使用查询的访问者设计模式不太熟悉。
我想向解析器发送一个查询，如下所示：“从c中选择a，b，其中d>5”，并得到结果：

选择子句中的所有字段名称（已完成）

将表名输入到FROM子句中（已完成）

将列名称、操作数和表达式输入到WHERE子句中

这就是我正在实施的代码：

    @Override
public QueryDescription parse() throws StandardException {

    SQLParser parser = new SQLParser();

    StatementNode stmt = parser.parseStatement(sql);

    Visitor v = new Visitor() {

        @Override
        public boolean visitChildrenFirst(Visitable arg0) {
            // TODO Auto-generated method stub
            return false;
        }

        @Override
        public Visitable visit(Visitable arg0) throws StandardException {

            // Temporary stores the QueryDescription parameters
            StatementEnum se = null;
            String fromTable = null;
            String[] fields = null;

            if(arg0 instanceof CursorNode) {
                CursorNode cn = (CursorNode) arg0;

                // print out what statement is been declared in sql query
                System.out.println("Statement: " + cn.statementToString());

                // temporarly stores the statement
                String statement = cn.statementToString();

                // creates the right StatementEnum
                if(statement == "CREATE TABLE") {
                    se = StatementEnum.CREATE_TABLE;
                } else if(statement == "INSERT") {
                    se = StatementEnum.INSERT;
                } else if(statement == "SELECT") {
                    se = StatementEnum.SELECT;
                } else if(statement == "DROP TABLE") {
                    se = StatementEnum.DROP_TABLE;
                }
            } 

            description = new QueryDescription(se, fromTable, fields);

            return arg0;
        }

        @Override
        public boolean stopTraversal() { return false; }

        @Override
        public boolean skipChildren(Visitable arg0) throws StandardException { return false; }
    };  
    stmt.accept(v);

    // TODO remove, only for debug purpose
    stmt.treePrint();

    return description;
}

这就是QueryDescription类代码：

public class QueryDescription {

    /* Member variables: */
    private QueryTypeEnum queryType;
    private StatementEnum statement;
    private String fromTable;
    private String[] fields;


    /* Constructors: */
    /**
     * 
     * @param statement
     * @param fromTable
     * @param fields
     */
    public QueryDescription(StatementEnum statement, String fromTable, String[] fields) {
        this.statement = statement;
        this.fromTable = fromTable;
        this.fields = fields;
    }


    /* Methods: */
    /**
     * Analyze which type of query is the one passed by parameter and assigns the right queryTypeEnum
     */
    public void assignType() {

        switch(statement) {

            case CREATE_TABLE:
                break;

            case SELECT:
                if(fields[0] == "allFields")
                    queryType = QueryTypeEnum.DUMP;
                else {
                    // TODO risolvere questione del WHERE
                    queryType = QueryTypeEnum.SELECT_FROM;
                }
                break;

            case UPDATE:
                break;

            case INSERT:
                break;

            case DROP_TABLE:
                break;
        }
    }


    /* Getters and Setter: */
    /**
     * 
     * @return the queryType
     */
    public QueryTypeEnum getQueryType() {
        return queryType;
    }

    /**
     * 
     * @return the statement
     */
    public StatementEnum getStatement() {
        return statement;
    }

    /**
     * 
     * @return the from table
     */
    public String getFromTable() {
        return fromTable;
    }

    /**
     * 
     * @return the fields
     */
    public String[] getFields() {
        return fields;
    }
}

---

您的代码没有显示

QueryDescription

类的功能，但我可以猜测

在处理where子句时，需要寻找三种类型的节点：

• BinaryLogicalOperatorNode

  -这有AND，OR，IS运算符，用于分隔WHERE子句中的各个子句

---

• BinaryOperatorNode

  -这有个人>，非常感谢您的快速回答，我想进一步了解如何检测where子句中的左右术语，就像treePrint（）方法可以做的那样：查询：“从c中选择a，b，其中d>5”结果：leftOperator:com.foundationdb.sql.parser。ColumnReference@3f3aef95columnName:表名：null类型：null RightOperator:com.foundationdb.sql.parser。NumericConstantNode@36473fa1值：5类型：整数不为空

  Visitor v = new Visitor() {
      List<String> fromTable = new ArrayList<String>();
      List<String> fields = new ArrayList<String>();
  
      // other Visitor methods go here, not copied for conciseness. 
  
      @Override
      public Visitable visit(Visitable arg0) throws StandardException {
          // other code from your visit() method goes here
          // 
          if (arg0 instanceof FromBaseTable) {
             FromBaseTable table = (FromBaseTable)arg0;
             fromTable.append(table.getTableName());
          } else if (arg0 instanceof ColumnReference) {
             ColumnReference column = (ColumnReference) arg0;
             fields.append(column.getColumnName())
          }
          // Remove the call to create QueryDescription
      }
      public QueryDescription getQueryDescription() {
          return new QueryDescription(se, fromTable, fields)
      }
  }
  

  stmt.accept(v);
  QueryDescription description = v.getQueryDescription();