Null 值的 Java Criteria 构建器

Question

我使用了java标准生成器，这是我的代码

     RepositoryFactory.emf=Persistence.createEntityManagerFactory("onezero");
            String Symbol = "EURUSD";
            TradingHistory tradingHistorys = RepositoryFactory.getTradingHistoryRepo().findPriceEmpty(Symbol);
            String symbols = tradingHistorys.getSymbol();
            Date created = tradingHistorys.getCreated_at();

public TradingHistory findPriceEmpty( final String Symbol) throws SQLException{
          WhereClause<TradingHistory> conditions = new WhereClause<TradingHistory>() {

            public void defineWhere(CriteriaBuilder criteriaBuilder, CriteriaQuery<TradingHistory> criteriaQuery,
                    Root<TradingHistory> root) {
                // TODO Auto-generated method stub

                criteriaQuery.select(root).where((criteriaBuilder.and(criteriaBuilder.equal(root.get("Symbol"), Symbol)
                        ,(criteriaBuilder.equal(root.get("Price"), null)))));
            }
        };
        return singleResult(conditions,null,0,1,0);

    }

当我使用is null()时

    public TradingHistory findPriceEmpty( final String Symbol) throws SQLException{
              WhereClause<TradingHistory> conditions = new WhereClause<TradingHistory>() {

                public void defineWhere(CriteriaBuilder criteriaBuilder, CriteriaQuery<TradingHistory> criteriaQuery,
                        Root<TradingHistory> root) {
                    // TODO Auto-generated method stub

                    criteriaQuery.select(root).where((criteriaBuilder.and(criteriaBuilder.equal(root.get("Symbol"), Symbol)
                            ,(criteriaBuilder.equal(root.get("Price").isNull(), root)))));
                }
            };
            return singleResult(conditions,null,0,1,0);

        }

我遇到了类似的错误

    java.lang.IllegalArgumentException: org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected AST node: is near line 1, column 157 [select generatedAlias0 from com.dxtr.hibernate.model.TradingHistory as generatedAlias0 where ( generatedAlias0.Symbol=:param0 ) and ( generatedAlias0.Price is null=generatedAlias0 )]

我的问题当price = null时如何搜索？因为当我使用该代码时，我收到错误 Java 空指针异常。所以我们有问题......

请帮我解决这个问题

Answer 1

看起来您会使用isNull()如以下示例所示:

public TradingHistory findPriceEmpty( final String Symbol) throws SQLException{
          WhereClause<TradingHistory> conditions = new WhereClause<TradingHistory>() {

            public void defineWhere(CriteriaBuilder criteriaBuilder, CriteriaQuery<TradingHistory> criteriaQuery,
                    Root<TradingHistory> root) {                criteriaQuery.select(root).where((criteriaBuilder.and(criteriaBuilder.equal(root.get("Symbol"), Symbol),(criteriaBuilder.isNull(root.get("Price")))));
            }
        };
        return singleResult(conditions,null,0,1,0);

希望有帮助。如果您遇到更多问题，请发表评论。