java - JSF、JPA 应用程序中的 SQL 查询错误

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

在跟踪中我发现:

Caused by: java.lang.IllegalArgumentException: An exception occurred while creating a query in EntityManager: Exception Description: Syntax error parsing [SELECT * FROM PRODUCT WHERE CATEGORY='Humano']. [22, 22] A select statement must have a FROM clause. [7, 7] The left expression is missing from the arithmetic expression. [9, 22] The right expression is not an arithmetic expression

有什么想法吗？我的目标是刷新网页中的 JSF 数据表。

---

根据@Ilya 的回答编辑了我的代码，现在我得到了这个异常

Caused by: java.lang.IllegalArgumentException: An exception occurred while creating a query in EntityManager: Exception Description: Problem compiling [SELECT p FROM PRODUCT p WHERE CATEGORY='Humano']. [14, 21] The abstract schema type 'PRODUCT' is unknown. [30, 38] The identification variable 'CATEGORY' is not defined in the FROM clause.

---

应@Ilya 的要求，我发布了我的 Product 类:编辑:在注释中添加了@Table。

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 + " ]";
   }

}

感谢您到目前为止的帮助。在这里，我在我的应用程序中发布了另一个查询，它运行正常:

   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) FROM子句中需要为表指定别名，SELECT子句中应包含别名
Product 应该是一个实体

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

如果 PRODUCT 不是一个实体，你应该创建 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) 当 JPA 无法定位您的实体类时，JPA 抛出 "Unknown abstract schema type" 错误
同时将实体添加到 persistence.xml

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

3) 添加@Table 注释到您的@Entity
4) 正如我在 documentation 中看到的那样, JPQL 区分大小写。

With the exception of names of Java classes and properties, queries are case-insensitive. So SeLeCT is the same as sELEct is the same as SELECT, but org.hibernate.eg.FOO and org.hibernate.eg.Foo are different, as are foo.barSet and foo.BARSET.

所以JPQL查询应该是

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