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POExceptions: System.NullReferenceException while trying to create relation between tables in dataSet
 

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  1. POExceptions: System.NullReferenceException while trying to create relation between tables in dataSet
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    <p>using C#, .net framework 4.5, VS 2012</p> <p>Try to create simple relation between tables in data set, but got System.NullReferenceException, as I can see on MSDN, it's mean <code>occurs when you try to reference an object in your code that does not exist</code>. But, think i create all required objects.</p> <p>My code below:</p> <pre><code> //create place for storing all tables from data base private DataSet myDS = new DataSet("AutoLot"); //command builders for easy way access to tables private SqlCommandBuilder sqlCInventory; private SqlCommandBuilder sqlCOrders; private SqlCommandBuilder sqlCCustomers; //adapters for each table private SqlDataAdapter sqlAInventory; private SqlDataAdapter sqlAOrders; private SqlDataAdapter sqlACustomers; //connection string private string cnStr = string.Empty; public MainForm() { InitializeComponent(); //get connection string from .config file cnStr = ConfigurationManager.ConnectionStrings["AutoLotSqlProvider"].ConnectionString; //create adapters sqlACustomers = new SqlDataAdapter("Select * From Customers", cnStr); sqlAInventory = new SqlDataAdapter("Select * From Inventory", cnStr); sqlAOrders = new SqlDataAdapter("Select * From Orders", cnStr); //automatic generate commands sqlCCustomers = new SqlCommandBuilder(sqlACustomers); sqlCInventory = new SqlCommandBuilder(sqlAInventory); sqlCOrders = new SqlCommandBuilder(sqlAOrders); //add table to data Set sqlAInventory.Fill(myDS); sqlAOrders.Fill(myDS); sqlACustomers.Fill(myDS); //create relationship between tables BuildTableRelationShip(); //create DataSourse for datGrids on UI dataGridViewCustomer.DataSource = myDS.Tables["Inventory"]; dataGridViewOrders.DataSource = myDS.Tables["Orders"]; dataGridViewCustomer.DataSource = myDS.Tables["Customers"]; } </code></pre> <p>and here I got exception</p> <pre><code> private void BuildTableRelationShip() { //create object of relationShips DataRelation dr = new DataRelation("CustomersOrders", //name of relation myDS.Tables["Customers"].Columns["CustID"], //main columns myDS.Tables["Orders"].Columns["OrderID"]); //related columns myDS.Relations.Add(dr); //second relation dr = new DataRelation("InventoryOrder", myDS.Tables["Inventory"].Columns["CarID"], myDS.Tables["Orders"].Columns["OrderID"]); //add relations to dataset myDS.Relations.Add(dr); } </code></pre> <p>Why i got this Null reference Exception? What i miss?</p> <p><strong>EDIT</strong></p> <p><img src="https://i.stack.imgur.com/YKRs1.png" alt="enter image description here"></p>
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    1. This table or related slice is empty.
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    1. USgbk
    1. USgbk
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    1. This table or related slice is empty.
    1. This table or related slice is empty.
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      1. POExceptions: System.NullReferenceException while trying to create relation between tables in dataSet
      1. This table or related slice is empty.
      1. VTUpMod
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      1. POExceptions: System.NullReferenceException while trying to create relation between tables in dataSet
      1. This table or related slice is empty.
      1. VTUpMod
    1. COWhy don't you set a breakpoint in `BuildTableRelationShip` and step through the code until you hit the null reference exception? You can mouseover variables to see their values and/or store "watch variables" in a `Watch` window
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      1. POExceptions: System.NullReferenceException while trying to create relation between tables in dataSet
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    2. CODo you have a connection string called `AutoLotSqlProvider` ? `ConfigurationManager.ConnectionStrings["AutoLotSqlProvider"]`
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      1. POExceptions: System.NullReferenceException while trying to create relation between tables in dataSet
      1. USta.speot.is
    3. COyes, i have cnStr - it's in config file
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      1. POExceptions: System.NullReferenceException while trying to create relation between tables in dataSet
      1. USgbk
 

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