Entity Passed to WebAPI 2 Method is being Inserted and linked to existing entity

Question

I have the following classes (simplified for breivity);

   public partial class Stock 
{
    [Column("StockId")]
    [JsonProperty(PropertyName = "stockid")]
    public int ID { get; set; }
    public DateTime Date { get; set; }
    public int Quantity { get; set; }

    [JsonProperty(PropertyName = "devicecode")]
    public DeviceTypes Device { get; set; }
}

public partial class DeviceTypes
{
    [Column("id")]
    [JsonProperty(PropertyName = "devicetypeid")]
    public int ID { get; set; }
    public string DeviceType { get; set; }
}

just for fullness VS shows the table composition to be as follows;

 CREATE TABLE [dbo].[Stocks] (
    [StockId]     INT            IDENTITY (1, 1) NOT NULL,
    [Date]        DATETIME       NOT NULL,
    [Quantity]    INT            NOT NULL,
    [Device_ID]   INT            NULL,
    CONSTRAINT [PK_dbo.Stocks] PRIMARY KEY CLUSTERED ([StockId] ASC),
    CONSTRAINT [FK_dbo.Stocks_dbo.DeviceTypes_Device_ID] FOREIGN KEY ([Device_ID]) REFERENCES [dbo].[DeviceTypes] ([id])
);

CREATE TABLE [dbo].[DeviceTypes] (
    [id]         INT          IDENTITY (1, 1) NOT NULL,
    [DeviceType] VARCHAR (50) NOT NULL,
    CONSTRAINT [PK_Table1] PRIMARY KEY CLUSTERED ([id] ASC)
);

Now when I pass across for example

Stock objStock = new Stock();
objStock.Device = new DeviceTypes { ID = deviceid };
objStock.Date = DateTime.UtcNow;
objStock.Quantity = quantity;

to the api method which is as follows;

    public IHttpActionResult Post([FromBody]Stock stock)
    {
        //done as a double check 
        var deviceType = _Service.GetDeviceType(stock.Device.ID);
        stock.Device = deviceType;

        _Service.Insert(stock);

        return Ok(stock.ID);
    }

i.e. the object is hitting the API post method, however,everytime it is inserting a new DeviceType instead of linking to the valid one?

I have tried with and without getting the DeviceType from the db with no joy.

Can someone tell me what I am doing wrong here please?

Thanks in advance.

One thing we have noticed is that the GetServiceType is actually spinning up its own context and not the injected _service context (from the stock perspective) maybe this coul dbe causing the issue? if so does anyone have any ideas how to resolve it? — Matthew Flynn, Sep 02 '15 at 10:56
Very related: http://stackoverflow.com/questions/29721538/violation-of-primary-key-entity-framework-code-first/29721938#29721938 — Jeroen Vannevel, Sep 02 '15 at 11:30

score 1 · Answer 1 · answered Sep 02 '15 at 11:18

This is because EF thinks you are also passing along a new DeviceTypes object. You could add an identifier to this DeviceTypes object in your stock object which holds the ID of the pre-existing DeviceTypes object:

public partial class Stock 
{
    [Column("StockId")]
    [JsonProperty(PropertyName = "stockid")]
    public int ID { get; set; }
    public DateTime Date { get; set; }
    public int Quantity { get; set; }

    [JsonProperty(PropertyName = "devicecode")]
    public DeviceTypes Device { get; set; }
    [ForeignKey("Device")]
    public int DeviceTypesId {get; set;} // new field, holds existing devicetypes id
}

And then pass the stock object:

Stock objStock = new Stock();
objStock.DeviceTypesId = deviceid;
objStock.Date = DateTime.UtcNow;
objStock.Quantity = quantity;

Where deviceid is the id of the DeviceTypes object that already exists in the database.

Entity Passed to WebAPI 2 Method is being Inserted and linked to existing entity

1 Answers1