如何解决您是否需要在“启动”中为连接字符串的所有DI添加服务?
我在应用程序中使用数据库,因此需要访问存储在appsettings.json
文件中的连接字符串。在Startup.cs
文件中多次添加服务似乎很麻烦,而我每次都在做同样的事情。由于我有一个连接字符串,需要在随后在Blazor页面上使用的类中使用该连接字符串,因此我尝试制作一个提供服务的连接字符串:
public class ConnectionStringService
{
public string DataDB { get; set; }
}
//In Startup.cs
services.Configure<ConnectionStringService>(Configuration.GetSection("ConnectionStrings"));
services.AddScoped<ConnectionStringService>();
//I don't want a billion services.AddScoped<>(),one for every time I want to use a connection string,because it would get messy.
并尝试如下使用它:
public class SearchesTimeline
{
[Inject]
private ConnectionStringService connectionStrings { get; }
//private readonly ConnectionStringService connectionStrings;
//public SearchesTimeline(IOptions<ConnectionStringService> options)
//{
// connectionStrings = options.Value;
//}
public async Task<List<List<Timelineinfo>>> GetTimeline(string? current,int? dateChange,string? date)
{
if (current != null && dateChange != null)
{
date = Convert.ToDateTime(current).AddDays((double)dateChange).ToString("yyyy-MM-dd");
}
//This line is being executed
else if (date == null | string.IsNullOrWhiteSpace(Extensions.GetQueryParm("d")))
{
date = DateTime.Today.ToString("yyyy-MM-dd");
}
else
{
date = Extensions.GetQueryParm("d");
}
for (int i = 0; i < 7; i++)
{
//get data
DataAccess data = new DataAccess();
var query = "SELECT t.TimelineinfoId From timelineinfo t where t.date = " + dates[i].ToString("yyyy-MM-dd") + ";";
dateData[i] = await data.LoadData<Timelineinfo,dynamic>(query,new { },connectionStrings.DataDB);
//Here,where I access connectionStrings.DataDB,I get the error
}
//more code stuff
}
}
//On the blazor page:
SearchesTimeline searches = new Searches.SearchesTimeline();
[Parameter]
public string? current { get; set; }
[Parameter]
public string? date { get; set; }
protected override async Task OnInitializedAsync()
{
await searches.GetTimeline(current,date);
}
public async Task NextWeek()
{
await searches.GetTimeline(current,+7,date);
}
public async Task PrevWeek()
{
await searches.GetTimeline(current,date);
}
但是当我尝试运行它时,我得到了NullReferenceException:“对象引用未设置为对象的实例。”因此此代码无法正常工作。
是否可以为我所有的连接字符串需求配置一项服务,并以与上述类似的方式使用它?
解决方法
services.Configure<ConnectionStringService>(Configuration.GetSection("ConnectionStrings"));
此行之后,您无需再将类型添加到DI中。您可以使用IOptions 接口获取值。像这样:
[Inject] private IOptions<ConnectionStringService> connectionStrings { get; }
,然后可以通过访问对象的Value属性来使用它:
connectionStrings.Value
,
我最终要做的是制作一个静态函数,该函数将在需要的地方返回连接字符串。我将Startup.cs
文件更改为包含:
public static string ConnectionString { get; private set; }
public void Configure(IApplicationBuilder app,IWebHostEnvironment env)
{
//Add alongside whatever else you have in Configure()
ConnectionString = Configuration["ConnectionStrings:DataDB"];
}
函数真的很简单,只是:
public static string GetConnectionString()
{
return Startup.ConnectionString; //returns DataDB connection string
}
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