Java 在Spring、Hibernate和PostgreSQL中插入时在列中生成时间戳

我正在学习Spring、Hibernate和PostgreSQL。我有一个具有时间戳字段的实体。此时间戳的数据库列称为

datecreated

此时间戳应自动生成，但不会自动生成。插入记录时，只生成空值，而不是日期

我尝试了互联网上多种解决方案的组合，但没有成功。我试过这个：

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这就是我得到的：

如何让它生成时间戳？ 这是一个项目文件Image.java模型、pom.xml、import.sql ddl、hibernate.cfg.xml文件：

java

---

pom.xml

---

hibernate.cfg.xml

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org.postgresql.Driver
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org.hibernate.dialogue.postgresql95dialogue
1.
创造
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20
2.
1800
150

如果您使用JPA或本机hibernate方法从应用程序中进行插入，prePersist和其他@createTimeStamp钩子可以工作。如果您只是从应用程序上下文之外运行insert，那么hibernate就不可能知道正在运行什么DML，因此永远不会调用挂钩。如果您希望在运行insert时从外部执行该操作，那么create的时间戳应该自动填充，您需要添加表级DDL指令。 例如：

altertable mytable ALTER COLUMN datecreated SET DEFAULT now（）

现在，关于hibernate的自动DDL功能，xml属性
create
从实体定义而不是DML生成DDL。因此，您还可以将默认时间戳值嵌入相关实体的列定义中，如下所示：

@Column(name="datecreated", columnDefinition="TIMESTAMP DEFAULT CURRENT_TIMESTAMP")

这将确保在创建表时，使用hibernate设置的auto DDL属性应用定义

希望这能澄清，如果您使用JPA或本机hibernate方法在应用程序中进行插入，prePersist和其他@createTimeStamp钩子可以工作。如果您只是从应用程序上下文之外运行insert，那么hibernate就不可能知道正在运行什么DML，因此永远不会调用挂钩。如果您希望在运行insert时从外部执行该操作，那么create的时间戳应该自动填充，您需要添加表级DDL指令。
例如：
altertable mytable ALTER COLUMN datecreated SET DEFAULT now（）

现在，关于hibernate的自动DDL功能，xml属性
create
从实体定义而不是DML生成DDL。因此，您还可以将默认时间戳值嵌入相关实体的列定义中，如下所示：

@Column(name="datecreated", columnDefinition="TIMESTAMP DEFAULT CURRENT_TIMESTAMP")

这将确保在创建表时，使用hibernate设置的auto DDL属性应用定义

希望这能澄清
您的意思是什么时候import.sql applicated dateCreated值不在表中？您是如何获得import.sql文件的？当您在管理数据库交互（通常是DAO）的类中调用persiste（）或save（）时，日志中生成的就是这个吗？@code\uyes@EdBighands此文件是项目的一部分。该项目基于教程。该文件在教程中是这样描述的：“3.填充数据库表定义实体后，可以将import.sql放在项目结构的resources文件夹下，以便Hibernate可以在表中填充sql语句。”您的意思是当import.sql applied dateCreated值不在表中时？您是如何获得import.sql文件的？当您在管理数据库交互（通常是DAO）的类中调用persiste（）或save（）时，日志中生成的就是这个吗？@code\uyes@EdBighands此文件是项目的一部分。该项目基于教程。该文件在教程中是这样描述的：“3.填充数据库表定义实体后，可以将import.sql放在项目结构的resources文件夹下，以便Hibernate可以在表中填充sql语句。”
@CreationTimestamp
@Column
private Date dateCreated = new Date();

@CreationTimestamp
@Temporal(TemporalType.TIMESTAMP)
@Column
private Date dateCreated = new Date();

@Temporal(TemporalType.TIMESTAMP)
@Column
private Date dateCreated = new Date();

@Temporal(TemporalType.TIMESTAMP)
@Column(updatable = false)
private Date dateCreated = new Date();

@CreationTimestamp
@Temporal(TemporalType.TIMESTAMP)
@Column(updatable = false)
private Date dateCreated = new Date();

@CreationTimestamp
@Temporal(TemporalType.TIMESTAMP)
@Column(updatable = false)
private Date dateCreated;

@CreationTimestamp
@Temporal(TemporalType.TIMESTAMP)
@Column(updatable = false)
private Date dateCreated;

@PrePersist
protected void onCreate() {
    dateCreated = new Date();
}

package com.howtodoinjava.demo.spring.domain;

import javax.persistence.*;
import java.util.Date;
import org.hibernate.annotations.CreationTimestamp;

@Entity
@Table(name = "images")
public class Image {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, length = 300)
    private String title;

    @Column(nullable = false)
    private String url;

    @Column(nullable = false)
    private String author;

    @CreationTimestamp
    @Column
    private Date dateCreated = new Date();

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public Date getDate() {
        return dateCreated;
    }

    public void setDate(Date dateCreated) {
        this.dateCreated = dateCreated;
    }

    public Image() {}

    public Image(Long id, String title, String url, String author) {
        this.id = id;
        this.title = title;
        this.url = url;
        this.author = author;
    }

    @Override
    public String toString() {
        return "Post{" +
                "id=" + id +
                ", title='" + title + '\'' +
                ", url='" + url + '\'' +
                ", author=" + author +
                ", date=" + dateCreated +
                '}';
    }
}

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.bitMiners</groupId>
    <artifactId>pdf-app</artifactId>
    <version>0.0.1</version>
    <packaging>war</packaging>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <aspect.version>1.9.2</aspect.version>
        <jackson.version>2.9.8</jackson.version>
        <hibernate.version>5.4.2.Final</hibernate.version>
        <hibernate.validator.version>6.0.13.Final</hibernate.validator.version>
        <c3p0.version>0.9.5.2</c3p0.version>
    </properties>

    <dependencies>
        
        <!-- servlets and jps -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.apache.tiles</groupId>
            <artifactId>tiles-extras</artifactId>
            <version>3.0.8</version>
            <exclusions>
                <exclusion>
                    <groupId>org.slf4j</groupId>
                    <artifactId>jcl-over-slf4j</artifactId>
                </exclusion>
                <exclusion>
                    <groupId>jboss</groupId>
                    <artifactId>javassist</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

        <dependency>
            <groupId>commons-fileupload</groupId>
            <artifactId>commons-fileupload</artifactId>
            <version>1.3.3</version>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-io</artifactId>
            <version>1.3.2</version>
        </dependency>

        <!--hibernate-->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>${hibernate.version}</version>
            <exclusions>
                <exclusion>
                    <groupId>org.javassist</groupId>
                    <artifactId>javassist</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
            <version>${hibernate.version}</version>
        </dependency>
        <!-- Hibernate-C3P0 Integration -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-c3p0</artifactId>
            <version>${hibernate.version}</version>
        </dependency>

        <!-- c3p0 -->
        <dependency>
            <groupId>com.mchange</groupId>
            <artifactId>c3p0</artifactId>
            <version>${c3p0.version}</version>
        </dependency>

        <!-- validation -->
        <dependency>
            <groupId>org.hibernate.validator</groupId>
            <artifactId>hibernate-validator</artifactId>
            <version>${hibernate.validator.version}</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.34</version>
        </dependency>

        <!-- for rest services -->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>${jackson.version}</version>
        </dependency>

        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.3</version>
        </dependency>

        <!-- For Aop -->
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjrt</artifactId>
            <version>${aspect.version}</version>
        </dependency>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjweaver</artifactId>
            <version>${aspect.version}</version>
        </dependency>

        <!-- To Send Email -->
        <dependency>
            <groupId>com.sun.mail</groupId>
            <artifactId>javax.mail</artifactId>
            <version>1.5.4</version>
        </dependency>


        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-core</artifactId>
            <version>5.2.0.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>5.2.0.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-tx</artifactId>
            <version>5.2.0.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-orm</artifactId>
            <version>5.2.0.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-web</artifactId>
            <version>5.2.0.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-config</artifactId>
            <version>5.2.0.RELEASE</version>
        </dependency>

        <!--logging-->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.8.2</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>2.8.2</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-web -->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-web</artifactId>
            <version>2.13.3</version>
        </dependency>


        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.30</version>
        </dependency>

        <!-- PostgreSQL -->
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <version>42.2.16</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context-support</artifactId>
            <version>5.1.3.RELEASE</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.springframework.security/spring-security-taglibs -->
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-taglibs</artifactId>
            <version>5.1.2.RELEASE</version>
        </dependency>

    </dependencies>

    <build>
        <!-- To define the plugin version in your parent POM -->
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-surefire-plugin</artifactId>
                    <version>2.22.1</version>
                </plugin>
            </plugins>
        </pluginManagement>
        <plugins>
            <!-- To use the plugin goals in your POM or parent POM -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.22.1</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.2.2</version>
            </plugin>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

-- ...
INSERT INTO images (title, url, author) VALUES ('lanszaft', 'https://i.imgur.com/sZ64fVI.jpg', 'Oskar Kamiński');
INSERT INTO images (title, url, author) VALUES ('kobieta w kapeluszu', 'https://i.imgur.com/spMsvHe.png', 'Pablo Picasso');

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <session-factory>
        <property name="hibernate.archive.autodetection">class,hbm</property>
        <property name="hibernate.show_sql">true</property>
        <property name="hibernate.connection.url">jdbc:postgresql://localhost:5432/postgres</property> <!-- BD Mane -->

        <property name="hibernate.connection.driver_class">org.postgresql.Driver</property> 
        <property name="hibernate.connection.username">user32</property>
        <property name="hibernate.connection.password">pa$$word</property>
        <property name="hibernate.dialect">org.hibernate.dialect.PostgreSQL95Dialect</property>
        <property name="hibernate.connection.pool.size">1</property>

        <property name="hibernate.hbm2ddl.auto">create</property>
        <property name="hibernate.enable_lazy_load_no_trans">true</property>
        <property name="hibernate.jdbc.lob.non_contextual_creation">true</property>
        <property name="hibernate.c3p0.min_size">5</property>
        <property name="hibernate.c3p0.max_size">20</property>
        <property name="hibernate.c3p0.acquire_increment">2</property>
        <property name="hibernate.c3p0.timeout">1800</property>
        <property name="hibernate.c3p0.max_statements">150</property>

        <mapping class="com.howtodoinjava.demo.spring.domain.User"/>
        <mapping class="com.howtodoinjava.demo.spring.domain.Authority"/>
        <mapping class="com.howtodoinjava.demo.spring.domain.AuthorityType"/>
        <mapping class="com.howtodoinjava.demo.spring.domain.Image"/>


    </session-factory>
</hibernate-configuration>

@Column(name="datecreated", columnDefinition="TIMESTAMP DEFAULT CURRENT_TIMESTAMP")