Question

我想以升序显示组合框中的不同年份。但是combox中的输出似乎是重复的，重复的，因为它显示了数据库列的所有元素，但我想只显示列的不同数据。我究竟做错了什么？？我之前在php中做过简单的数据库查询。我知道这很简单但我不是以正确的顺序解决查询，我猜。

我的代码如下。

/*
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 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

package my_ui;

import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
import java.io.Serializable;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
import javax.persistence.Transient;

/**
 *
 * @author enjal
 */
@Entity
@Table(name = "production", catalog = "data2", schema = "")
@NamedQueries({
    @NamedQuery(name = "Production.findAll", query = "SELECT p FROM Production p"),
    @NamedQuery(name = "Production.findByProductionId", query = "SELECT p FROM Production p WHERE p.productionId = :productionId"),
    @NamedQuery(name = "Production.findByCropId", query = "SELECT p FROM Production p WHERE p.cropId = :cropId"),
    @NamedQuery(name = "Production.findByLocationId", query = "SELECT p FROM Production p WHERE p.locationId = :locationId"),
    @NamedQuery(name = "Production.findByArea", query = "SELECT p FROM Production p WHERE p.area = :area"),
    @NamedQuery(name = "Production.findByProductionAmount", query = "SELECT p FROM Production p WHERE p.productionAmount = :productionAmount"),
    @NamedQuery(name = "Production.findByYieldAmount", query = "SELECT p FROM Production p WHERE p.yieldAmount = :yieldAmount"),
    @NamedQuery(name = "Production.findByYearOfProduction", query = "SELECT DISTINCT p FROM Production p WHERE p.yearOfProduction = :yearOfProduction ORDER BY p.yearOfProduction ASC" )})
//SELECT DISTINCT year_of_production FROM `production` ORDER BY year_of_production ASC
public class Production implements Serializable {
    @Transient
    private PropertyChangeSupport changeSupport = new PropertyChangeSupport(this);
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "production_id")
    private Integer productionId;
    @Basic(optional = false)
    @Column(name = "crop_id")
    private int cropId;
    @Basic(optional = false)
    @Column(name = "location_id")
    private String locationId;
    @Basic(optional = false)
    @Column(name = "area")
    private double area;
    @Basic(optional = false)
    @Column(name = "production_amount")
    private String productionAmount;
    @Basic(optional = false)
    @Column(name = "yield_amount")
    private double yieldAmount;
    @Basic(optional = false)
    @Column(name = "year_of_production")
    private String yearOfProduction;

    public Production() {
    }

    public Production(Integer productionId) {
        this.productionId = productionId;
    }

    public Production(Integer productionId, int cropId, String locationId, double area, String productionAmount, double yieldAmount, String yearOfProduction) {
        this.productionId = productionId;
        this.cropId = cropId;
        this.locationId = locationId;
        this.area = area;
        this.productionAmount = productionAmount;
        this.yieldAmount = yieldAmount;
        this.yearOfProduction = yearOfProduction;
    }

    public Integer getProductionId() {
        return productionId;
    }

    public void setProductionId(Integer productionId) {
        Integer oldProductionId = this.productionId;
        this.productionId = productionId;
        changeSupport.firePropertyChange("productionId", oldProductionId, productionId);
    }

    public int getCropId() {
        return cropId;
    }

    public void setCropId(int cropId) {
        int oldCropId = this.cropId;
        this.cropId = cropId;
        changeSupport.firePropertyChange("cropId", oldCropId, cropId);
    }

    public String getLocationId() {
        return locationId;
    }

    public void setLocationId(String locationId) {
        String oldLocationId = this.locationId;
        this.locationId = locationId;
        changeSupport.firePropertyChange("locationId", oldLocationId, locationId);
    }

    public double getArea() {
        return area;
    }

    public void setArea(double area) {
        double oldArea = this.area;
        this.area = area;
        changeSupport.firePropertyChange("area", oldArea, area);
    }

    public String getProductionAmount() {
        return productionAmount;
    }

    public void setProductionAmount(String productionAmount) {
        String oldProductionAmount = this.productionAmount;
        this.productionAmount = productionAmount;
        changeSupport.firePropertyChange("productionAmount", oldProductionAmount, productionAmount);
    }

    public double getYieldAmount() {
        return yieldAmount;
    }

    public void setYieldAmount(double yieldAmount) {
        double oldYieldAmount = this.yieldAmount;
        this.yieldAmount = yieldAmount;
        changeSupport.firePropertyChange("yieldAmount", oldYieldAmount, yieldAmount);
    }

    public String getYearOfProduction() {
        return yearOfProduction;
    }

    public void setYearOfProduction(String yearOfProduction) {
        String oldYearOfProduction = this.yearOfProduction;
        this.yearOfProduction = yearOfProduction;
        changeSupport.firePropertyChange("yearOfProduction", oldYearOfProduction, yearOfProduction);
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (productionId != null ? productionId.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 Production)) {
            return false;
        }
        Production other = (Production) object;
        if ((this.productionId == null && other.productionId != null) || (this.productionId != null && !this.productionId.equals(other.productionId))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "my_ui.Production[ productionId=" + yearOfProduction + " ]";
    }

    public void addPropertyChangeListener(PropertyChangeListener listener) {
        changeSupport.addPropertyChangeListener(listener);
    }

    public void removePropertyChangeListener(PropertyChangeListener listener) {
        changeSupport.removePropertyChangeListener(listener);
    }

}

Answer 1

我想以升序显示组合框中的不同年份。但是组合框中的输出似乎是重复的，重复的，因为它显示了数据库列的所有元素，但我只想显示列的不同数据

你说这是你用来完成的查询

@NamedQuery(name = "Production.findByYearOfProduction", 
            query = "SELECT DISTINCT p FROM Production p 
                     WHERE p.yearOfProduction = :yearOfProduction
                     ORDER Bp.yearOfProduction ASC" )})

此查询的问题在于它用于通过yearOfProduction查找生产实体列表。所以说你在1990年使用这个查询。这意味着1990年生产的任何生产实体都是结果集的一部分。因此，您将看到的唯一生产年份是1990年。

您想要的只是单个列中的不同值，而实际的生产实体并不一定关注。所以你的查询看起来应该更像

SELECT DISTINCT p.yearOfProduction 
FROM Production p
ORDER BY p.yearOfProduction ASC

返回值应该只是不同年份的列表，并且与Production实体没有任何关联。您可能希望对代码进行一些重构，调用此查询将返回List<String>。这就是您要用于组合框的列表，而不是List<Production>。你应该在哪里进行这种重构？我无法告诉您，因为您没有提供调用此查询的代码。

注意：那么你应该做的是创建一个单独的@NamedQuery，以及你现在拥有的那个，我想你想要保留一个不同的组合框，从第一个组合框中选择一年后，第二个是当年的所有生产实体。另请注意，您的toString仅列出生产年份。因此，如果您想要在第二个组合框中对Production实体进行其他表示，您也应该更改它。

在Netbeans中自动创建实体时，请记住，它将为实体的每个属性创建findAll查询和查询findByXxx查询。就是这样。所有查询都是使用一个属性作为查找匹配结果的参数来返回生产实体列表。您需要的任何其他返回类型（在本例中为字符串列表）或不同的参数查询，您需要创建自定义查询

从java中的swing组合框中的数据库绑定

1 个答案: