英文:
How to insert a struct with nil field to mongo?
问题
我正在尝试将一个结构体插入到MongoDB中。首先，我从一个API获取JSON数据，并将数据赋值给一个结构体。有些字段可能为nil。然后，我将结构体插入到MongoDB中。问题是，插入后，所有字段都被初始化了。例如，我有一个如下的结构体：
type VirtualMachine struct {
VirtualMachineID utils.SUUID `bson:"VirtualMachineID"`
Cdroms []*VM.VirtualMachineCdrom `bson:"Cdroms"`
CpuAllocatedMHz int `bson:"CpuAllocatedMHz"`
Name string `bson:"Name"`
}
如果我得到的JSON数据如下：
{
"VirtualMachineID": '16as4df663a',
"Cdroms": null,
"CpuAllocatedMHz": 1666,
"Name": 'VMName'
}
在将其放入MongoDB后，null字段变成了一个空数组。我需要避免这种情况。omitempty并没有帮助，因为如果提供的字段恰好是一个空数组而不是null，它也会跳过该字段。
起初我以为是因为指针的原因，但后来我发现对所有数据类型都是如此。简而言之，如果为nil，mgo会将其转换为零值。
我觉得我在这里漏掉了什么，因为如果mgo将所有nil值都按设计转换为零值，那就太奇怪了。
英文:
I am trying to insert a struct to mongo. Firstly I get the data from an API as JSON and assign the data to a struct. Some fields might be nil. After that I insert the struct to mongoDB. So the problem I get is that when inserted, all the fields are initialized. For example I have a struct like this:
type VirtualMachine struct {
VirtualMachineID utils.SUUID `bson:"VirtualMachineID"`
Cdroms []*VM.VirtualMachineCdrom `bson:"Cdroms"`
CpuAllocatedMHz int `bson:"CpuAllocatedMHz"`
Name string `bson:"Name"`
}
If I get Json data like this
{
"VirtualMachineID":'16as4df663a',
"Cdroms":null,
"CpuAllocatedMHz":1666,
"Name":'VMName'
}
after I put it to mongo, the null field becomes an empty array. I need to avoid that. 'omitempty' did not help because it skips the field as well if the provided field happens to be an empty array and not null.
Firstly I thought it was because of the pointers, but later I found that the same happens to all data types. Shortly, if its nil, mgo converts it to its zero value.
I think I am missing something here, because it would be weird if mgo converts all nil values to their zero values by design.
答案1
得分: 1
尝试使用*[]*VM.VirtualMachineCdrom（如果你不需要元素实际上是指针，可以只使用*[]VM.VirtualMachineCdrom）。nil切片等于长度为零的切片，但nil的切片指针不等于零。
英文:
Try *[]*VM.VirtualMachineCdrom (or just *[]VM.VirtualMachineCdrom if you don't actually need the elements to be pointers). A nil slice == a zero length slice, but a nil pointer to a slice does not.
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