CODEWITHSUNDEEP
javascriptc#asp.netajax
Pvxtotal
Pvxtotal

Reputation: 89

AJAX Call to Update table goes Null - ASP.NET

I'm trying to update my table using Ajax Call through this code

 var customer = {};
        customer.CustomerId = row.find(".CustomerId").find("span").html();
        customer.Nome = row.find(".Nome").find("span").html();
        customer.Tipo = row.find(".Tipo").find("span").html();
        customer.NCM = row.find(".NCM").find("span").html();
        customer.Contabil = row.find(".Contabil").find("span").html();

        $.ajax({
            type: "POST",
            url: "/Home/UpdateCustomer",
            data: '{customer:' + JSON.stringify(customer) + '}',
            contentType: "application/json; charset=utf-8",
            dataType: "json"
        });
    });

But when I click to update the value it returns a System.NullReferenceException, I can't see where I'm doing wrong.

Here's my Controller Code

 public ActionResult UpdateCustomer(Customer customer)
    {
        using (CustomersEntities entities = new CustomersEntities())
        {
            Customer updatedCustomer = (from c in entities.Customers
                                        where c.CustomerId == customer.CustomerId
                                        select c).FirstOrDefault();
            updatedCustomer.Nome = customer.Nome;
            updatedCustomer.Tipo = customer.Tipo;
            updatedCustomer.NCM = customer.NCM;
            updatedCustomer.Contabil = customer.Contabil;
            entities.SaveChanges();
        }

        return new EmptyResult();
    }

Upvotes: 0

Views: 195

Answers (2)

Tetsuya Yamamoto
Tetsuya Yamamoto

Reputation: 24957

This AJAX callback below actually passed JSON string containing JSON object, which is wrong and causing customer contains null value which throwing NullReferenceException (it is strongly advised to put null check before using EF entity context):

$.ajax({
    type: "POST",
    url: "/Home/UpdateCustomer",
    data: '{customer:' + JSON.stringify(customer) + '}', // this is wrong 
    contentType: "application/json; charset=utf-8",
    dataType: "json"
});

Instead of passing JSON string like that, just use data: JSON.stringify(customer) or simply passing entire object directly with data: customer and remove contentType setting:

$.ajax({
    type: "POST",
    url: "/Home/UpdateCustomer",
    data: customer, 
    dataType: "json",
    success: function (result) {
        // do something
    }
});

Regarding second issue which selected data from table query is not updated, it depends on auto-tracking setting from EF. If auto-tracking is disabled, you need to set EntityState.Modified before using SaveChanges():

if (customer != null)
{
    using (CustomersEntities entities = new CustomersEntities())
    {
        Customer updatedCustomer = (from c in entities.Customers
                                    where c.CustomerId == customer.CustomerId
                                    select c).FirstOrDefault();

        updatedCustomer.Nome = customer.Nome;
        updatedCustomer.Tipo = customer.Tipo;
        updatedCustomer.NCM = customer.NCM;
        updatedCustomer.Contabil = customer.Contabil;

        // if EF auto-tracking is disabled, this line is mandatory 
        entities.Entry(updatedCustomer).State = System.Data.Entity.EntityState.Modified;
        entities.SaveChanges();
    }
}

Notes:

1) You can see all methods to update existing data with EF in this reference.

2) This fiddle contains sample to make AJAX request from a table contents.

Upvotes: 1

Winter
Winter

Reputation: 191

System.NullReferenceException revealed the value updatedCustomer or customer is null.You need check which is null.

And when you want to update a enity in EF,you need add code like :

    context.Entry(existingBlog).State = EntityState.Modified;

Howerver,Why you need Query A Entity befor update?I guess you want to do this:

    public ActionResult UpdateCustomer(Customer customer)
    {
      using (CustomersEntities entities = new CustomersEntities())
       {
          entities.Entry(customer).State = EntityState.Modified;
          entities.SaveChanges();
       }
       return new EmptyResult();
    }

Upvotes: 1

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