EF Core 映射关系及取数据（急等高手）

我现在准备用EF Core从现有的数据库里取数据出来，有三张表：

其中，一个JobHeader可以包含多个JobOperation,关联键是JobNum, 同样的一个JobOperation,可以包含多个OprTransactions，关联键是JobNum+OpCode

请问我怎样用EF Core来定义映射关系并取值呢？

public class JobHeader
{
[Key]
public string JobNum { get; set; }
public string PartNum { get; set; }
}

public class JobOperation
{
[Key]
public int Id { get; set; }
public string JobNum { get; set; }
public string OpCode { get; set; }

}

public class OprTransactions
{
[Key]
public int Id { get; set; }
public string JobNum { get; set; }
public string OpCode { get; set; }
public string TransType { get; set; }
}

希望取值的内容如下：

{
"jobNum": "000025172-0009",
"partNum": "CIB-75-00024KT-A",
"JobOperation": [
{
"jobNum": "000025172-0009",
"opCode": "NF01",
"OprTransactions": [
{
"id": 1,
"jobNum": "000025172-0009",
"opCode": "NF01",
"transType": "OPRSTART",
},
{
"id": 2,
"jobNum": "000025172-0009",
"opCode": "NF01",
"transType": "OPREND",
}
]
},
{
"jobNum": "000025172-0009",
"opCode": "NF34",
"OprTransactions": [
{
"id": 3,
"jobNum": "000025172-0009",
"opCode": "NF34",
"transType": "OPRSTART",
}
]
}
]
}