Question

如何获取一列的DISTINCT结果集。在这种情况下productType。

我已经失去了几个小时，而且已经累了。我不知道为什么这么难:(

我得到的错误是：

exception

javax.servlet.ServletException: javax.el.PropertyNotFoundException: The class 'java.lang.String' does not have the property 'productType'.
root cause

javax.el.PropertyNotFoundException: The class 'java.lang.String' does not have the property 'productType'.

我在ProductFacade中的查询

public List<Product> getDistinctProduct()
{
    return em.createQuery( "SELECT DISTINCT p.productType FROM Product p" )
            .getResultList();
}

我的产品实体

@Entity 
@Table(name = "product")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "Product.findAll", query = "SELECT p FROM Product p"),
    @NamedQuery(name = "Product.findByProductId", query = "SELECT p FROM Product p WHERE p.productId = :productId"),
    @NamedQuery(name = "Product.findByName", query = "SELECT p FROM Product p WHERE p.name = :name"),
    @NamedQuery(name = "Product.findByPrice", query = "SELECT p FROM Product p WHERE p.price = :price"),
    @NamedQuery(name = "Product.findByDescription", query = "SELECT p FROM Product p WHERE p.description = :description"),
    @NamedQuery(name = "Product.findByQuantityInStock", query = "SELECT p FROM Product p WHERE p.quantityInStock = :quantityInStock"),
    @NamedQuery(name = "Product.findByImageUrl", query = "SELECT p FROM Product p WHERE p.imageUrl = :imageUrl"),
    @NamedQuery(name = "Product.findByProductType", query = "SELECT p FROM Product p WHERE p.productType = :productType")})
public class Product implements Serializable 
{
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "product_id")
    private Integer productId;
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 45)
    @Column(name = "name")
    private String name;
    @Basic(optional = false)
    @NotNull
    @Column(name = "price")
    private float price;
    @Size(max = 1024)
    @Column(name = "description")
    private String description;
    @Basic(optional = false)
    @NotNull
    @Column(name = "quantity_in_stock")
    private int quantityInStock;
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 256)
    @Column(name = "image_url")
    private String imageUrl;
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 16)
    @Column(name = "product_type")
    private String productType;
    @ManyToMany(mappedBy = "productCollection")
    private Collection<Wishlist> wishlistCollection;
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "product")
    private Collection<OrderProduct> orderProductCollection;
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "product")
    private Collection<Review> reviewCollection;

    public Product() {
    }

    public Product(Integer productId) {
        this.productId = productId;
    }

    public Product(Integer productId, String name, float price, String description, int quantityInStock, String imageUrl, String productType) {
        this.productId = productId;
        this.name = name;
        this.price = price;
        this.description = description;
        this.quantityInStock = quantityInStock;
        this.imageUrl = imageUrl;
        this.productType = productType;
    }

    public Integer getProductId() {
        return productId;
    }

    public void setProductId(Integer productId) {
        this.productId = productId;
    }

    public String getName() {
        return name;
    }

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

    public float getPrice() {
        return price;
    }

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

    public String getDescription() {
        return description;
    }

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

    public int getQuantityInStock() {
        return quantityInStock;
    }

    public void setQuantityInStock(int quantityInStock) {
        this.quantityInStock = quantityInStock;
    }

    public String getImageUrl() {
        return imageUrl;
    }

    public void setImageUrl(String imageUrl) {
        this.imageUrl = imageUrl;
    }

    public String getProductType() {
        return productType;
    }

    public void setProductType(String productType) {
        this.productType = productType;
    }

    @XmlTransient
    @JsonIgnore
    public Collection<Wishlist> getWishlistCollection() {
        return wishlistCollection;
    }

    public void setWishlistCollection(Collection<Wishlist> wishlistCollection) {
        this.wishlistCollection = wishlistCollection;
    }

    @XmlTransient
    @JsonIgnore
    public Collection<OrderProduct> getOrderProductCollection() {
        return orderProductCollection;
    }

    public void setOrderProductCollection(Collection<OrderProduct> orderProductCollection) {
        this.orderProductCollection = orderProductCollection;
    }

    @XmlTransient
    @JsonIgnore
    public Collection<Review> getReviewCollection() {
        return reviewCollection;
    }

    public void setReviewCollection(Collection<Review> reviewCollection) {
        this.reviewCollection = reviewCollection;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (productId != null ? productId.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof Product)) {
            return false;
        }
        Product other = (Product) object;
        if ((this.productId == null && other.productId != null) || (this.productId != null && !this.productId.equals(other.productId))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "com.onemore.entity.Product[ productId=" + productId + " ]";
    }

}

Answer 1

我是个菜鸟。

当我试图在我的JSP页面上处理结果时，我有

<c:forEach var="productList" items="${productTypeList}">
<option value="${productList.productType}">${productList.productType}</option>
</c:forEach>

我什么时候应该

<c:forEach var="productTypeList" items="${productTypeList}">             
<option value="${productTypeList}">${productTypeList}</option>
</c:forEach>

如何让DISTINCT处理JPA查询

1 个答案: