休眠生成额外的表

Question

我有一个这样的实体

@Entity

@Table(name = "past_price")

public class PastPrice {

    @Id

    private String symbol;

    @OneToMany(fetch = FetchType.EAGER,cascade = CascadeType.ALL)

    private Set<Price> prices = null;

    public String getSymbol() {

        return symbol;

    }

    public void setSymbol(String symbol) {

        this.symbol = symbol;

    }

    public Set<Price> getPrices() {

        return prices;

    }

    public void setPrices(Set<Price> prices) {

        this.prices = prices;

    }

}

实体是这样的Price

@Entity

public class Price {

    @Id

    @Temporal(TemporalType.TIMESTAMP)

    private Date date;

    private String price;

    public Date getDate() {

        return date;

    }

    public void setDate(Date date) {

        this.date = date;

    }

    public String getPrice() {

        return price;

    }

    public void setPrice(String price) {

        this.price = price;

    }

}

我试图做的是，创建一个带有名称的表，它与实体有关系。我有休眠属性，所以每当我运行这个时，都会创建3个表和.但我只是试图创建2个表和.任何帮助将不胜感激。谢谢past_priceOneToManyPricespring.jpa.hibernate.ddl-auto=update1. past_price2. past_price_prices3. pricepast_priceprice

Answer 1

使用@JoinColumn告诉休眠在价格表中创建列，并将其用于联接。将您的代码更改为以下内容：@OneToMany(fetch = FetchType.EAGER,cascade = CascadeType.ALL)@JoinColumn(name = "fk_past_price")private Set<Price> prices = null;这将在价格表中创建一个名为 fk_past_price 的列，并且不会创建第三个表。P.S.：如果没有充分的理由使用单向关联，请使用双向关联。如下图所示：@Entity@Table(name = "past_price")public class PastPrice {&nbsp; &nbsp; @Id&nbsp; &nbsp; private String symbol;&nbsp; &nbsp; @OneToMany(mappedBy = "pastPrice", cascade = CascadeType.ALL, fetch = FetchType.EAGER)&nbsp; &nbsp; private Set<Price> prices = null;&nbsp; &nbsp; public String getSymbol() {&nbsp; &nbsp; &nbsp; &nbsp; return symbol;&nbsp; &nbsp; }&nbsp; &nbsp; public void setSymbol(String symbol) {&nbsp; &nbsp; &nbsp; &nbsp; this.symbol = symbol;&nbsp; &nbsp; }&nbsp; &nbsp; public Set<Price> getPrices() {&nbsp; &nbsp; &nbsp; &nbsp; return prices;&nbsp; &nbsp; }&nbsp; &nbsp; public void setPrices(Set<Price> prices) {&nbsp; &nbsp; &nbsp; &nbsp; this.prices = prices;&nbsp; &nbsp; }}价格：@Entitypublic class Price {&nbsp; &nbsp; @Id&nbsp; &nbsp; @Temporal(TemporalType.TIMESTAMP)&nbsp; &nbsp; private Date date;&nbsp; &nbsp; private String price;&nbsp; &nbsp; @ManyToOne&nbsp; &nbsp; @JoinColumn(name = "past_price_symbol", nullable = false)&nbsp; &nbsp; private PastPrice pastPrice;&nbsp; &nbsp; public PastPrice getPastPrice() {&nbsp; &nbsp; &nbsp; return pastPrice;&nbsp; &nbsp; }&nbsp; &nbsp; public void setPastPrice(PastPrice pastPrice) {&nbsp; &nbsp; &nbsp; this.pastPrice = pastPrice;&nbsp; &nbsp; }&nbsp; &nbsp; public Date getDate() {&nbsp; &nbsp; &nbsp; &nbsp; return date;&nbsp; &nbsp; }&nbsp; &nbsp; public void setDate(Date date) {&nbsp; &nbsp; &nbsp; &nbsp; this.date = date;&nbsp; &nbsp; }&nbsp; &nbsp; public String getPrice() {&nbsp; &nbsp; &nbsp; &nbsp; return price;&nbsp; &nbsp; }&nbsp; &nbsp; public void setPrice(String price) {&nbsp; &nbsp; &nbsp; &nbsp; this.price = price;&nbsp; &nbsp; }}

Answer 2

您应该添加“mappedBy”来声明哪个字段是相关表。还在价格实体中添加 ManyToOne。价格实体 ：@ManyToOne(fetch = FetchType.EAGER)@JoinColumn("past_price_fk")private PastPrice pastPrice;往年价格实体 ：@OneToMany(fetch = FetchType.EAGER,cascade = CascadeType.ALL, mappedBy = "pastPrice")private Set<Price> prices = null;

Answer 3

实际上，问题是您没有为实体提供其他映射。休眠如何识别与 ？休眠无法（但我不确定）在 中存储相关ID的数组。PricePastPricePrice默认情况下，如果您只需要2个表，则需要在中添加字段：Price@ManyToOne(...)private PastPrice pastPrice;在本例中，在“价格休眠”表中，生成 id 为“父”价格的 colymn。因此，对于当前映射，2个表就足够了。这将是这样的工作：select * from Price p join PastPrice pp on pp.id = p.past_price