英文:
save and loading custom types
问题
我有一个自定义类型 map[string]map[string]string，尝试将其保存在Google Datastore中，保存操作正常工作。然而，加载函数报错 assignment to entry in nil map。
// Address 表示地址
type Address map[string]map[string]string
上面的类型是一个 map 的 map[string]string，用于保存不同类型的地址。
// Load 函数从 PropertyLoaderInterface 帮助 Datastore 加载该对象
func (a *Address) Load(dp []datastore.Property) error {
for _, property := range dp {
(*a)[property.Name] = util.InterfaceToMapString(property.Value)
}
return nil
}
在加载函数中，我对 Address 进行了解引用，它是一个 map 的 map[string]string，它保存了以下示例 JSON 格式的数据。
"Company":{
"physicalAddress": "",
"postalAddress": "",
"physicalCity": "",
"postalCity": "",
"physicalCode": "",
"postalCode": "",
"physicalCountry": "",
"postalCountry": ""
}
下面的保存函数工作正常，并且数据被存储在 Datastore 中。然而，加载函数却有一个棘手的 bug。
// Save 函数从 PropertyLoaderInterface 帮助 Datastore 保存该对象
func (a *Address) Save() ([]datastore.Property, error) {
properties := []datastore.Property{}
for name, value := range *a {
properties = append(properties, datastore.Property{
Name: name,
NoIndex: true,
Value: util.MapToJSONString(value),
})
}
return properties, nil
}
Address 结构的工作加载函数
func (a *Address) Load(dp []datastore.Property) error {
*a = make(Address)
for _, property := range dp {
(*a)[property.Name] = util.InterfaceToMapString(property.Value)
}
return nil
}
英文:
I have a custom type map[string]map[string]string am trying to save in Google Datastore, the save works as expected. However the load functions complains about assignment to entry in nil map
//Address represents address
type Address map[string]map[string]string
Type above is a map of map[string]string, target at saving different address types.
//Load function from PropertyLoaderInterface helps datastore load this object
func (a *Address) Load(dp []datastore.Property) error {
for _, property := range dp {
(*a)[property.Name] = util.InterfaceToMapString(property.Value)
}
return nil
}
In the load function I deference the Address which is a map of map[string]string, it saves the following example JSON format.
"Company":{
"physicalAddress": "",
"postalAddress": "",
"physicalCity": "",
"postalCity": "",
"physicalCode": "",
"postalCode": "",
"physicalCountry": "",
"postalCountry": ""
}
Save function below works well and data is store in datastore. The Load is however rather a tricky bugger.
//Save function from PropertyLoaderInterface helps datastore save this object
func (a *Address) Save() ([]datastore.Property, error) {
propertise := []datastore.Property{}
for name, value := range *a {
propertise = append(propertise, datastore.Property{Name: name,
NoIndex: true,
Value: util.MapToJSONString(value)})
}
return propertise, nil
}
Working load for Address struct
func (a *Address) Load(dp []datastore.Property) error {
*a = make(Address)
for _, property := range dp {
(*a)[property.Name] = util.InterfaceToMapString(property.Value)
}
return nil
}
答案1
得分: 2
首先，关于声明 - https://stackoverflow.com/a/42901715/4720042
接下来，我认为你应该使用自定义结构体来实现这个目的。
即使你仍然想使用map[string]map[string]string，你也不能给一个在映射中没有明确定义的字段赋值，比如property.Name。
如果你计划在以后添加元素，你必须使用make来初始化该映射。
英文:
First, regarding the declarations - https://stackoverflow.com/a/42901715/4720042
Next, I feel you should instead use a custom struct for this purpose.
Even if you still want to use a map[string]map[string]string, you cannot assign to a field in a map that hasn't been explicitly defined viz. property.Name
You have to initialize that map with make if you plan on adding the elements later.
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