为什么输入模型在asp.net核心操作中为空

Question

I am submitting an order to my API.

Normally, it works fine. But sometimes, the inputModel is null.

Why would this occur?

public async Task<Order> NewAsync(OrderInput input)

Answer 1

The input model will be null in the controller when the InputModel does not match the actual parameters passed to it.

To be clear: the controller does not care if additional parameters are passed to it, it will simply ignore them.

But if there is a "required" parameter, such as:

public int TypeId{get;set;}

and this is not provided, then the entire input model will be null.

If TypeId is truely optional, then make it nullable, and then the input model will just set it to null.

public int? TypeId{get;set;} 

To summarize: the controller has been passed a null value for an InputModel for which the InputModel does not allow null. The result is the entire inputModel will be null when it is processed.

This can be frustrating as no exception is thrown, all you get is a null model.

The fix is to compare the post parameters in the browser with the Model and find which parameters is null that should not be. This happens to me far more often than I would care to admit, and each time, I have to stop and figure this out again, so I thought I would go ahead and post this here to remind myself next time.