JSF,JPA应用程序中的SQL Query错误

Question

我的应用程序中的查询有问题.这是执行查询的查询方法:

public List<Product> obtainProductListByCategory(String category)
   {
      Query query = em.createQuery("SELECT p FROM PRODUCT p WHERE CATEGORY='" + category + "'");
      List<Product> ret = query.getResultList();

      if (ret == null)
      {
         return new ArrayList<Product>();
      }
      else
      {
         return ret;
      }
   } 

这是错误: javax.ejb.EJBException

在我看到的踪迹中:

引发者:java.lang.IllegalArgumentException:在EntityManager中创建查询时发生异常:异常描述:语法错误解析[SELECT*FROM PRODUCT WHERE CATEGORY ='Humano'].[22,22] select语句必须有一个FROM子句.[7,7]算术表达式中缺少左表达式.[9,22]正确的表达式不是算术表达式

有任何想法吗？我的目标是在我的网页中刷新JSF数据表.

---

根据@Ilya的回答编辑了我的代码,现在我得到了这个例外

引起:java.lang.IllegalArgumentException:在EntityManager中创建查询时发生异常:异常描述:编译问题[SELECT p FROM PRODUCT p WHERE CATEGORY ='Humano'].[14,21]抽象模式类型'PRODUCT'是未知的.[30,38]在FROM子句中没有定义标识变量'CATEGORY'.

---

根据@Ilya的要求,我发布了我的Product课程:编辑:将@Table添加到注释中.

package model;

import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;


@Table
@Entity
public class Product implements Serializable, IProduct
{
   private static final long serialVersionUID = 1L;
   @GeneratedValue(strategy = GenerationType.AUTO)
   @Id
   private String name;
   private int stock;
   private float price;
   private String category;
   private String description;

  @Override 
  public String getDescription() {
        return description;
    }


  public void setDescription(String description) {
        this.description = description;
    }


   public Product()
   {
   }


   public Product(String name, int stock, float price, String category, String description)
   {
      this.name = name;
      this.stock = stock;
      this.price = price;
      this.category = category;
      this.description = description;
   }





   @Override
   public String getName()
   {
      return name;
   }


   public void setName(String name)
   {
      this.name = name;
   }


   @Override
   public float getPrice()
   {
      return price;
   }


   public void setPrice(float price)
   {
      this.price = price;
   }


   @Override
   public int getStock()
   {
      return stock;
   }


   public void setStock(int stock)
   {
      this.stock = stock;
   }


   @Override
   public int hashCode()
   {
      return name.hashCode();
   }


   @Override
   public boolean equals(Object object)
   {
      if (!(object instanceof Product))
      {
         return false;
      }
      Product other = (Product) object;
      if (name.equals(other.getName()))
      {
         return true;
      }
      return false;
   }

   @Override
   public String getCategory()
   {
      return category;
   }

   @Override
   public String toString()
   {
      return "Marketv2.model.Product[ name=" + name + " ]";
   }

}

感谢你目前的帮助.在这里,我在我的应用程序中发布另一个查询,它正常工作:

   public void removeProduct(Product g)
   {
      Query q = em.createQuery("SELECT x FROM BasketItem x WHERE x.product.name = '" + g.getName() + "'");
      List<BasketItem> bItems = q.getResultList();
      for (BasketItem i : bItems)
      {
         em.remove(i);
      }

      q = em.createQuery("DELETE FROM Product x WHERE x.name = '" + g.getName() + "'");
      q.executeUpdate();
   }
}

Answer 1

1)您应该为FROM子句中的表指定别名,而SELECT子句应该包含别名
Product应该是一个实体

em.createQuery("SELECT p FROM Product p WHERE p.category='" + category + "'");   

如果PRODUCT不是实体,您应该创建nativeQuery

em.createNativeQuery("SELECT p FROM PRODUCT p WHERE p.CATEGORY='" + category + "'");  

EntityManager :: createQuery用于JPQL(Java持久性查询语言)
EntityManager :: createNativeQuery用于SQL

2)"Unknown abstract schema type" 当JPA无法找到您的实体类时,JPA抛出错误还将实体
添加到persistence.xml

 <persistence-unit ...>
        <class>com.package.Product</class>  

3)添加@Table注释@Entity
4)正如我在文档中看到的,JPQL区分大小写.

除Java类和属性的名称外,查询不区分大小写.所以SeLeCT与sELEct和SELECT相同,但是org.hibernate.eg.FOO和org.hibernate.eg.Foo是不同的,foo.barSet和foo.BARSET也是如此.

所以JPQL查询应该是

SELECT p FROM Product p WHERE p.category = '...