我正在做正确的加载吗？ （雄辩）

时间：2017-12-28 13:01:46

标签： php laravel orm eloquent

我有一个方法需要从三个相关模型中提取信息。我有一个可行的解决方案，但我担心我仍然遇到N + 1查询问题（也在寻找解决方案，我可以检查我是否渴望正确加载）。

这三个模型是Challenge，Entrant，User。

挑战模型包含：

 /**
 * Retrieves the Entrants object associated to the Challenge
 * @return \Illuminate\Database\Eloquent\Relations\HasMany
 */
public function entrants()
{
    return $this->hasMany('App\Entrant');
}

参赛者模型包含：

     /**
     * Retrieves the Challenge object associated to the Entrant
     * @return \Illuminate\Database\Eloquent\Relations\BelongsTo
     */
    public function challenge()
    {
        return $this->belongsTo('App\Challenge', 'challenge_id');
    }

    /**
     * Retrieves the User object associated to the Entrant
     * @return \Illuminate\Database\Eloquent\Relations\BelongsTo
     */
    public function user()
    {
        return $this->belongsTo('App\User', 'user_id');
    }

和用户模型包含：

 /**
 * Retrieves the Entrants object associated to the User
 * @return \Illuminate\Database\Eloquent\Relations\HasMany
 */
public function entrants()
{
    return $this->hasMany('App\Entrant');
}

我尝试使用急切加载的方法如下所示：

/**
 * Returns an array of currently running challenges
 * with associated entrants and associated users
 * @return array
 */
public function liveChallenges()
{
    $currentDate = Carbon::now();
    $challenges = Challenge::where('end_date', '>', $currentDate)
        ->with('entrants.user')
        ->where('start_date', '<', $currentDate)
        ->where('active', '1')
        ->get();

    $challengesObject = [];
    foreach ($challenges as $challenge) {
        $entrants = $challenge->entrants->load('user')->sortByDesc('current_total_amount')->all();
        $entrantsObject = [];
        foreach ($entrants as $entrant) {
            $user = $entrant->user;
            $entrantsObject[] = [
                'entrant' => $entrant,
                'user' => $user
            ];
        }

        $challengesObject[] = [
            'challenge' => $challenge,
            'entrants' => $entrantsObject
        ];
    }

    return $challengesObject;
}

我觉得我遵循了文档推荐的内容：https://laravel.com/docs/5.5/eloquent-relationships#eager-loading

但不确定如何检查以确保我没有针对2进行N + 1查询。欢迎提供对代码的任何提示或建议，以及检查热切加载是否正常工作的方法。< / p>

2 个答案:

答案 0 :(得分：3)

使用Laravel Debugbar检查Laravel应用程序为每个请求创建的查询。

您的Eloquent查询应该只生成3个原始SQL查询，您需要确保此行不会生成N个其他查询：

2017-12-28 11:25:56.281  WARN 3101 --- [HelperThread-#0] c.m.v2.resourcepool.BasicResourcePool    : com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@1d7cb052 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception:

org.postgresql.util.PSQLException: This ResultSet is closed.
        at org.postgresql.jdbc2.AbstractJdbc2ResultSet.checkClosed(AbstractJdbc2ResultSet.java:2654) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2ResultSet.setFetchSize(AbstractJdbc2ResultSet.java:1771) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc4.Jdbc4Statement.createResultSet(Jdbc4Statement.java:39) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Statement$StatementResultHandler.handleResultRows(AbstractJdbc2Statement.java:211) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1773) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:257) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:512) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:374) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Connection.execSQLUpdate(AbstractJdbc2Connection.java:263) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Connection.getTransactionIsolation(AbstractJdbc2Connection.java:775) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at com.mchange.v2.c3p0.impl.NewPooledConnection.<init>(NewPooledConnection.java:120) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:181) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:147) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:202) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696) [mchange-commons-java-0.2.11.jar:0.2.11]

2017-12-28 11:25:56.282  WARN 3101 --- [HelperThread-#0] c.m.v2.resourcepool.BasicResourcePool    : Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@25e78fee is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests.
2017-12-28 11:25:56.282  WARN 3101 --- [HelperThread-#2] c.m.v2.resourcepool.BasicResourcePool    : com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@61136ebb -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception:

org.postgresql.util.PSQLException: This ResultSet is closed.
        at org.postgresql.jdbc2.AbstractJdbc2ResultSet.checkClosed(AbstractJdbc2ResultSet.java:2654) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2ResultSet.setFetchSize(AbstractJdbc2ResultSet.java:1771) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc4.Jdbc4Statement.createResultSet(Jdbc4Statement.java:39) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Statement$StatementResultHandler.handleResultRows(AbstractJdbc2Statement.java:211) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1773) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:257) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:512) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:374) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Connection.execSQLUpdate(AbstractJdbc2Connection.java:263) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Connection.getTransactionIsolation(AbstractJdbc2Connection.java:775) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at com.mchange.v2.c3p0.impl.NewPooledConnection.<init>(NewPooledConnection.java:120) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:181) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:147) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:202) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696) [mchange-commons-java-0.2.11.jar:0.2.11]

2017-12-28 11:25:56.293  WARN 3101 --- [HelperThread-#2] c.m.v2.resourcepool.BasicResourcePool    : Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@25e78fee is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests.
2017-12-28 11:25:56.311  WARN 3101 --- [ost-startStop-1] o.s.b.a.orm.jpa.DatabaseLookup           : Unable to determine jdbc url from datasource

org.springframework.jdbc.support.MetaDataAccessException: Could not get Connection for extracting meta data; nested exception is org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
        at org.springframework.jdbc.support.JdbcUtils.extractDatabaseMetaData(JdbcUtils.java:339) ~[spring-jdbc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.jdbc.support.JdbcUtils.extractDatabaseMetaData(JdbcUtils.java:366) ~[spring-jdbc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.boot.autoconfigure.orm.jpa.DatabaseLookup.getDatabase(DatabaseLookup.java:72) ~[spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at org.springframework.boot.autoconfigure.orm.jpa.JpaProperties.determineDatabase(JpaProperties.java:139) [spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at org.springframework.boot.autoconfigure.orm.jpa.JpaBaseConfiguration.jpaVendorAdapter(JpaBaseConfiguration.java:105) [spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration$$EnhancerBySpringCGLIB$$ee7fda69.CGLIB$jpaVendorAdapter$4(<generated>) [spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration$$EnhancerBySpringCGLIB$$ee7fda69$$FastClassBySpringCGLIB$$40f1d36d.invoke(<generated>) [spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228) [spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:358) [spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration$$EnhancerBySpringCGLIB$$ee7fda69.jpaVendorAdapter(<generated>) [spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_151]
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_151]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_151]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_151]
        at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:162) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:588) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1173) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1067) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:208) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1138) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:835) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:741) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:467) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1173) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1067) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:208) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1138) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:835) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:741) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:467) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1173) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1067) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) [spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1080) [spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:857) [spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543) [spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at org.springframework.boot.web.support.SpringBootServletInitializer.run(SpringBootServletInitializer.java:154) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at org.springframework.boot.web.support.SpringBootServletInitializer.createRootApplicationContext(SpringBootServletInitializer.java:134) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at org.springframework.boot.web.support.SpringBootServletInitializer.onStartup(SpringBootServletInitializer.java:87) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
        at org.springframework.web.SpringServletContainerInitializer.onStartup(SpringServletContainerInitializer.java:169) [spring-web-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5196) [catalina.jar:8.5.24]
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) [catalina.jar:8.5.24]
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:752) [catalina.jar:8.5.24]
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:728) [catalina.jar:8.5.24]
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734) [catalina.jar:8.5.24]
        at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:986) [catalina.jar:8.5.24]
        at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1857) [catalina.jar:8.5.24]
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_151]
        at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_151]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_151]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_151]
        at java.lang.Thread.run(Thread.java:748) [na:1.8.0_151]
        at java.lang.Thread.run(Thread.java:748) [na:1.8.0_151]
Caused by: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
        at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:80) ~[spring-jdbc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.jdbc.support.JdbcUtils.extractDatabaseMetaData(JdbcUtils.java:326) ~[spring-jdbc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        ... 74 common frames omitted
Caused by: java.sql.SQLException: Connections could not be acquired from the underlying database!
        at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:118) ~[mchange-commons-java-0.2.11.jar:0.2.11]
        at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:692) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:140) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:111) ~[spring-jdbc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:77) ~[spring-jdbc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
        ... 75 common frames omitted
Caused by: com.mchange.v2.resourcepool.CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source.
        at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1469) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:644) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:554) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutAndMarkConnectionInUse(C3P0PooledConnectionPool.java:758) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:685) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        ... 78 common frames omitted
Caused by: org.postgresql.util.PSQLException: This ResultSet is closed.
        at org.postgresql.jdbc2.AbstractJdbc2ResultSet.checkClosed(AbstractJdbc2ResultSet.java:2654) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2ResultSet.setFetchSize(AbstractJdbc2ResultSet.java:1771) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc4.Jdbc4Statement.createResultSet(Jdbc4Statement.java:39) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Statement$StatementResultHandler.handleResultRows(AbstractJdbc2Statement.java:211) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1773) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:257) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:512) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:374) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Connection.execSQLUpdate(AbstractJdbc2Connection.java:263) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at org.postgresql.jdbc2.AbstractJdbc2Connection.getTransactionIsolation(AbstractJdbc2Connection.java:775) ~[postgresql-9.1-901-1.jdbc4.jar:na]
        at com.mchange.v2.c3p0.impl.NewPooledConnection.<init>(NewPooledConnection.java:120) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:181) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:147) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:202) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870) ~[c3p0-0.9.5.2.jar:0.9.5.2]
        at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696) ~[mchange-commons-java-0.2.11.jar:0.2.11]

答案 1 :(得分：2)

当您执行->with('entrants.user')时，一旦到达->get()，它就会加载参赛者和用户。执行->load('user')时，它会运行另一个查询来获取用户。但是你不需要这样做，因为你在运行->with('entrants.user')时已经拉过它。

如果您使用->loadMissing('user')代替->load('user')，则应阻止冗余呼叫。

但是，如果您使用Collection methods，只需在声明$challenges的开头运行1个查询即可逃脱：

foreach ($challenges as $challenge) {
    // at this point, $challenge->entrants is a Collection because you already eager-loaded it
    $entrants = $challenge->entrants->sortByDesc('current_total_amount'); 
    // etc...

您不需要使用->load('user')，因为$challenge->entrants已填充了参赛者和相关用户。所以你可以利用Collection方法->sortByDesc()对php中的列表进行排序。

另外，您不需要运行->all()，因为这会将其转换为模型数组（您可以将其保留为模型集合并且仍然可以预先设置它）。

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