在Java中的swing组合框中从数据库进行绑定

Question

我想按升序在组合框中显示不同的年份。 但是combox中的输出似乎是重复的，因为它显示了数据库列的所有元素，但是我只想显示该列的不同数据。 我究竟做错了什么？？ 我只是在php中完成了简单的数据库查询。 我知道这很简单，但我想我不是以正确的顺序解决查询。

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

我想按升序在组合框中显示不同的年份。 但是组合框中的输出似乎是重复的，从某种意义上说，它显示了数据库列的所有元素，但是我只想显示列的不同数据

您说这是您用来完成该任务的查询

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

该查询的问题在于，它用于根据yearOfProduction查找列表Production实体。 假设您在1990年使用此查询。这意味着1990年生产的任何Production实体都属于结果集。 因此，您看到的唯一的生产年份是1990年。

您想要的只是单个列中的不同值，而实际的Production实体不一定要涉及。 所以您的查询应该更像

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

返回值应仅是不同年份的列表，并且与生产实体没有任何关系。 您可能需要对代码进行一些重构，在其中调用此查询将返回List<String> 。 这就是您要用于组合框的List<Production> ，而不是List<Production> 。 您应该在哪里进行重构？ 我不知道，因为您还没有提供调用此查询的代码。

注意：因此，您应该做的是创建一个单独的@NamedQuery，然后创建一个@NamedQuery，我想您可能想保留另一个组合框，也许是从第一个组合框中选择一年后，第二个组合框包含该年的所有生产实体。 还要注意，您的toString仅列出了生产年份。 因此，如果要在第二个组合框中显示生产实体的其他表示形式，则也应该更改它。

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一个findAll查询和一个findByXxx查询。 而已。 所有查询均旨在使用该属性作为查找匹配结果的参数来返回生产实体的列表。 您需要其他任何返回类型（在这种情况下为字符串列表）或其他参数查询，则需要创建一个自定义查询