Spring Data JPA中基于内部连接查询和接口的投影

Question

我正在使用Spring Data JPA运行MySql DB开发一个Spring MVC项目，其中有四个实体对象：旅行、费用、货币和基金。

下面是我的DB架构的可视化表示：

在ExpenseRepository接口中，我扩展了JpaRepository接口。

现在，我尝试运行一个本机SQL查询，在这里我将传递expenseId，并从费用表中获取费用和金额，从货币表中获取currency_name。（您可以看到，我必须执行两个内部联接才能获得currency_name。）

package com.binarycraftbd.ksktravelbackend.Repo

import com.binarycraftbd.ksktravelbackend.JoinQueries.ExpenseData
import com.binarycraftbd.ksktravelbackend.Model.Expense
import org.springframework.data.jpa.repository.JpaRepository
import org.springframework.data.jpa.repository.Query

interface ExpenseRepo : JpaRepository<Expense, Int> {


    @Query("select expense, amount from expense, currencyName from currency inner join fund on expense.fund_id=fund.id inner join currency on fund.currency_id=currency.id where expense.id=?1", nativeQuery = true)
    fun getCurrencyByExpId(expId:Int): ExpenseOutput

    interface ExpenseOutput{
        fun getExpense():String
        fun getAmount(): String
        fun getCurrencyname(): String
    }
}

This application has no explicit mapping for /error, so you are seeing this as a fallback.

Sat Sep 22 20:51:25 BDT 2018
There was an unexpected error (type=Internal Server Error, status=500).
could not extract ResultSet; SQL [n/a]; nested exception is org.hibernate.exception.SQLGrammarException: could not extract ResultSet

@Entity
@Table(name = "travel")
class Travel(
        @Id
        @GeneratedValue(strategy = GenerationType.SEQUENCE)
        val id: Int=0,
        val travelName: String="",

        @OneToMany(mappedBy = "travel")
        @JsonIgnore
        val funds: List<Fund> ?= null,

        @OneToMany(mappedBy = "travel")
        @JsonIgnore
        val expenses: List<Expense>?=null

)

@Entity
@Table(name = "currency")
class Currency(

        @Id
        @GeneratedValue(strategy = GenerationType.SEQUENCE)
        val id: Int=0,
        val currencyName: String="",

        @OneToMany(mappedBy = "currency")
        @JsonIgnore
        val funds: List<Fund>?=null
)

@Entity
class Fund(
        @Id
        @GeneratedValue(strategy = GenerationType.SEQUENCE)
        val id:Int=0,
        val fundName:String="",

        @OneToMany(mappedBy = "fund")
        @JsonIgnore
        val expenses: List<Expense>?= null,

        @ManyToOne
        val travel: Travel?=null,

        @ManyToOne
        val currency:Currency?=null
)

费用类别

@Entity
class Expense(


        @Id
        @GeneratedValue(strategy = GenerationType.SEQUENCE)
        val id:Int=0,
        val date:String="",
        val time:String="",
        val expense:String="",
        val amount:String="",
        val category:String="",

        @ManyToOne
        val travel: Travel?=null,

        @ManyToOne
        val fund: Fund?=null
)

如何解决这个问题？在ExpenserePository中编写查询代码是不正确的吗？还是Sql查询有问题？皮斯救命！！

Answer 1

Econ尝试在任何sql客户机中运行这个查询，例如，在将它嵌入到代码中之前。

我像下面一样重写了上面的查询，我发现了一些语法错误和非逻辑的东西。

select expense.expense, expense.amount, currency.currency_name  
from expense inner join fund on (expense.fund_id=fund.id)
inner join currency on (fund.currency_id=currency.id)
where expense.id=<replace this segment with a valid expenseId>