access dbcontext in custom Newtonsoft JsonConverter class

Question

I created an JsonConverter for mapping children entitys to list of ids in json for example childrens:[1,2,3]

public class IdsJsonConverter : JsonConverter
{ 
    public override bool CanConvert(Type objectType)
    {
        return objectType==typeof(ICollection);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        //problem convert ids back to entities because i can not get db context here so I unable to get the tracked entities from context
        return existingValue;
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        IEnumerable collection = (IEnumerable)value;
        List<long> ids = new List<long>();
        foreach (var item in collection)
        {
            dynamic itemCollection = (dynamic)item;
            ids.Add(itemCollection.ID);
        }
        //successful convert to list of ids 
        serializer.Serialize(writer, ids);
    }
}

the problem is i can not get db context in ReadJson() the dbcontext is added to the services container using the Scoped lifetime

 public void ConfigureServices(IServiceCollection services)
    {
        services.AddScoped((_) => new MyDatabase(Configuration.GetConnectionString("DefaultConnection")));

this is how I use IdsJsonConverter

    [JsonConverter(typeof(IdsJsonConverter))] 
    public virtual ICollection<TAG> TAGs { get; set; }

Can you save your IoC container as a static variable in some place. Then in your ReadJson, get that container and resolve your DbContext instance. — Kim Hoang, Dec 16 '16 at 04:00
I mean the IoC Container, not the static dbcontext. I am not sure about MVC CORE, but using AutoFac, you should have a container, and you can store that container somewhere to use. — Kim Hoang, Dec 16 '16 at 04:17
Your question maybe answer in this thread http://stackoverflow.com/questions/31863981/how-to-resolve-instance-inside-configureservices-in-asp-net-core — Kim Hoang, Dec 16 '16 at 04:20
This seems like a bad architectural decision. Why would a JSON serializer have anything to do with fetching data from a data store? — Tieson T., Dec 16 '16 at 04:35
because this Converter was convert entities to an simple number list, it need to convert back to tracked entities by reading database. — Charles Chou, Dec 16 '16 at 04:42

score 1 · Accepted Answer · edited Dec 16 '16 at 06:08

1

You can call below code in your ConfigureServices

var serviceProvider = services.BuildServiceProvider();

Then assign this serviceProvider as a static variable in some place. Eg: App.ServiceProvider.

In your ReadJson

App.ServiceProvider.GetService<MyDatabase>();

You need Microsoft.Framework.DependencyInjection for this to work.

edited Dec 16 '16 at 06:08

Charles Chou

179
1
15

answered Dec 16 '16 at 04:25

Kim Hoang

1,338
9
24

Is you mean store serviceProvider in somewhere static and I get my services by calling serviceProvider.GetService();? – Charles Chou Dec 16 '16 at 04:33
I am able to get the DbContext now, this way is simple and elegant. – Charles Chou Dec 16 '16 at 04:39

access dbcontext in custom Newtonsoft JsonConverter class

1 Answers1