在View Models中初始化查找的最佳实践

I have an Address View Model and I used to initialize the list of countries from the database in the view model creation, however I realized that each time I create the ViewModel somewhere, the list of countries is retrieved from the db without being used, so I though of three ways to do accomplish this:

我有一个地址视图模型，我曾经在视图模型创建中初始化数据库中的国家列表，但是我意识到每次在某处创建ViewModel时，都会从数据库中检索国家列表而不使用它，所以我有三种方法可以做到这一点：

Add the Countries initialization to the Address View Model Constructor, very costly
将Countries初始化添加到Address View Model Constructor，非常昂贵
Load the lookup from the controllers and then assign it to the view model and then load the view
从控制器加载查找，然后将其分配给视图模型，然后加载视图

Using lazy loading on the countries property, so the trip is made to the db only when the countries are required, something like this

在countries属性上使用延迟加载，因此只有在需要国家/地区时才会访问数据库，就像这样

    // Lazy loading
[ScriptIgnore]
private IEnumerable<SelectListItem> _Countries;
[ScriptIgnore]
public IEnumerable<SelectListItem> Countries { 
    get{
        if (_Countries.Count() > 0) return _Countries;
        else {
            using (var db = new AllegroDMContainer()) {
                var rCountries = db.Countries.ToList();
                _Countries = (from m in rCountries
                             select new SelectListItem {
                                 Text = m.Name + " (" + m.ISO + ")",
                                 Value = m.ID.ToString()
                             });
                return  _Countries;
            }
        }
    } 
    set{
        _Countries = value;
    } 
}

What do you guys think is the better approach here and the one that seems more natural?

你们认为这里更好的方法和看起来更自然的方法是什么？

1 个解决方案

#1

Add the Countries initialization to the Address View Model Constructor, very costly

将Countries初始化添加到Address View Model Constructor，非常昂贵

This is fine, assuming that you're passing a collection and not a DbContext.

假设您传递的是集合而不是DbContext，这很好。

Load the lookup from the controllers and then assign it to the view model and then load the view

从控制器加载查找，然后将其分配给视图模型，然后加载视图

This is the most common pattern I've seen.

这是我见过的最常见的模式。

Using lazy loading on the countries property, so the trip is made to the db only when the countries are required, something like this

在countries属性上使用延迟加载，因此只有在需要国家/地区时才会访问数据库，就像这样

This couples the ViewModel to the DAL, which is a bad thing. Don't do this.

这将ViewModel耦合到DAL，这是一件坏事。不要这样做。

#1