Why Is SQL Server Throwing This Error: Cannot Insert the Value Null into Column 'Id'

Why is SQL server throwing this error: Cannot insert the value NULL into column 'id'?

I'm assuming that id is supposed to be an incrementing value.

You need to set this, or else if you have a non-nullable column, with no default value, if you provide no value it will error.

To set up auto-increment in SQL Server Management Studio:

• Open your table in Design
• Select your column and go to Column Properties
• Under Indentity Specification, set (Is Identity)=Yes and Indentity Increment=1

SQL insert error: Cannot insert the value NULL into column 'Id'

According to your comment on the question above, the Id column is defined as:

[Id] NVARCHAR (128) NOT NULL 

And that's it. No default value, no identity/autoincrement, etc. Simply a character value which can not be NULL. But when you perform an insert you don't provide a value:

INSERT INTO Users (pinConfirmed,Factor,DateUtc,LockoutEnabled,AccessCount,EmailConfirmed)
values ('false', 'false','1/1/2018' ,'false','0','false')

That's why you get an error. NOT NULL means a value is required. You're not providing one.

You have a few options:

• Provide a value for the column when you INSERT
• Make the column generate its own value (this will depend on your RDBMS, for example in SQL Server you would make the column an IDENTITY or in MySQL you'd make it AUTOINCREMENT, though both of those are for integer columns, whereas yours is character data, so you'll need to change the data type as well)
• Allow NULL, which of course will only work once because this is a primary key column and values must be unique.

Cannot insert the value NULL into column 'id', table 'XXX'; column does not allow nulls. INSERT fails, despite using GenerationType.IDENTITY

What you are posting here is not a table definition in SQL DDL but an image. As far as I can tell from it though, the id column is not marked as "identity" as required by SQL Server, so this is why you are seeing the error.

C# System.Data.SqlClient.SqlException Cannot insert the value NULL into column ERROR FOREIGN KEY

Your error is in this function as I see :

public static void AddVehicle(string client_ID,string serial_Number, string Make, string Model, string 
Year, string Color)
{
    string insStmt = "INSERT INTO VEHICLE (client_ID,serial_Number, Make,  Model, Year, Color) 
    VALUES (@client_ID,@serial_Number, @Make, @Model, @Year, @Color)";
    SqlConnection conn = GetConnection();
    SqlCommand insCmd = new SqlCommand(insStmt, conn);
    insCmd.Parameters.AddWithValue("@client_ID", client_ID);
    insCmd.Parameters.AddWithValue("@serial_Number", serial_Number);
    insCmd.Parameters.AddWithValue("@Make", Make);
    insCmd.Parameters.AddWithValue("@Model", Model);
    insCmd.Parameters.AddWithValue("@Year", Year);
    insCmd.Parameters.AddWithValue("@Color", Color);

    try 
    { 
         conn.Open(); 
         insCmd.ExecuteNonQuery(); 
    }
    catch (SqlException ex) 
    {
         throw ex; 
    }
    finally 
    { 
         conn.Close(); 
    }
}

You are missing the client_ID in the insert SQL statement, hence you get the error of Client Id being null.

You need to pass client_ID to the Add Vehicle function or your function INSERT statement will definitely fail.

Cannot insert the value NULL into column X, column X does not allow nulls. INSERT fails.

Exactly! You aren't doing anything with Occupied and that is the problem. The column is specified to be NOT NULL but has no default value. You are not inserting a value, so it gets the default. The default default is NULL, and that is not allowed.

One simple solution is:

INSERT INTO tblGrave (GraveName, Occupied)
    SELECT Grave, 0
    FROM tblPlotsandOccupants;

This fixes your immediate problem, but will then you will get an error on PlotId.

A more robust solution would add a default value for the NOT NULL columns and declare the rest to be nullable (the default). Something like this:

CREATE TABLE tblGrave (
    GraveID INT IDENTITY (1,1) PRIMARY KEY,
    GraveName VARCHAR(MAX),
    GraveTypeID,
    PlotID INT,
    Occupied BIT NOT NULL DEFAULT 0
);

SqlException: Cannot insert the value NULL into column 'CarId', table 'AutoServiceDb.dbo.ServiceOrders'; column does not allow nulls. INSERT fails

It looks like you are not assigning the new 'entity' to your 'car' object you are trying to create...

var car = _context.Cars.Where(...).FirstOrDefault();
if (car == null)
{
    var entity = _context.Cars.Add(new Car
    {
       ...
    });
}

var serviceOrder = _context.Add(new ServiceOrder
{
   Client = client,
   Car = car, // <-- 'car' is still null when you assign it's value to the service order
   ...
}

Try adding something like this:

var car = _context.Cars.Where(...).FirstOrDefault();
if (car == null)
{
    car = new Car // Assign the new car to the null car variable.
    {
      ...
    };

    _context.Cars.Add(car); // Then add it to the context.
}

Because the 'ServiceOrder.Car' property is null when are trying to insert it into SQL the database tries to insert NULL into CarId.

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