How do i fix the core CRUD options?

Question

Got a issue with the core CRUD options from this C# app. See .zip file. How do i solve the bug? And what the reason why it's not working .... ? Used software and settings 1. MS Management Studio . Run sql script. 2. VS 2017 Connection for db. Add in fonfig file. Initial Catalog=RContactApp;Integrated Security=True;"/>

Manav Pandya · Answer

Hello I think problem is with connection string , if you are using password and username than provide it also And its suggested to always use Provider name at the end of connection string Try and debug solution and observe inner exception for that Than you will get to know where problem occur Thanks

Rajneesh Chaubey · Answer

Have you debug you code? What is the exact error you are getting?

Rajneesh Chaubey · Answer

hi, It is clearly visible that you are missing constructor in your ContactClass Just add below lines to your code:- public ContactClass() { }

Rajneesh Chaubey · Answer

When you are assigning result on button click, you are missing 'Note'. In Insert method you are passing parameter cmd.Parameters.AddWithValue( "@Note" , c.Note); But you are not assigning it on button click. This is where proble occuring. Just add this to your insert method: c.Note = txtBoxNote.Text;

love code · Answer

Except this one; Faild to add ... No othere errors That's the reason i uploaded the soursefiles.

Vijay Thapa · Answer

In your Insert Method , Instead of writing code in catch block. Please write the code inside try block. Hope it will fix your error. Thanks.

love code · Answer

Got a NullReferenceException and System.TypeInitializationException in this updated C# crud project. ContactClass c = new ContactClass(); generates these errors. What are the solutions for this errors and hy are they there? See code or .zip ContactClass.java using System; using System.Collections.Generic; using System.Configuration; using System.Data; using System.Data.SqlClient; using System.Linq; using System.Text; using System.Threading.Tasks; namespace Rcontact.RcontactClasses { class ContactClass { // Getter Setter properties // Acts as a data carrirer in the application public int ContactID { get; set; } public string FirstName { get; set; } public string LastName { get; set; } public string Phone { get; set; } public string Email { get; set; } public string Note { get; set; } public string Status { get; set; } static string myconnstrng = ConfigurationManager.ConnectionStrings[ "connstrng" ].ConnectionString; // Selecting data from database public DataTable Select() { // Step 1 Database connection SqlConnection conn = new SqlConnection(myconnstrng); DataTable dt = new DataTable(); try { // Step 2 Wrting SQL query string sql = "SELECT * FROM tbl_contact" ; // creating cmd using swql and conn SqlCommand cmd = new SqlCommand(sql, conn); // Creating SQL DataAdapater using cmd SqlDataAdapter adapter = new SqlDataAdapter(cmd); conn.Open(); adapter.Fill(dt); } catch (Exception ex) { } finally { conn.Close(); } return dt; } // inserting data into database public bool Insert(ContactClass c) { // Creating a default return type and setting its value to false bool isSuccess = false ; // Step 1: Connect database SqlConnection conn = new SqlConnection(myconnstrng); try { } catch (Exception ex) { // Step 2 Creating a SQL Quary to insert data string sql = "INSERT INTO tbl_contact(FirstName, LastName, Phone, Email, Note, Status) " + "(@FirstName, @LastName, @Phone, @Email, @Note, @Status" ; // Creatigin SQL command using sql and conn SqlCommand cmd = new SqlCommand(sql, conn); // Create Parameters tot add data cmd.Parameters.AddWithValue( "@FirstName" , c.FirstName); cmd.Parameters.AddWithValue( "@LasttName" , c.LastName); cmd.Parameters.AddWithValue( "@Phone" , c.Phone); cmd.Parameters.AddWithValue( "@Email" , c.Email); cmd.Parameters.AddWithValue( "@Note" , c.Note); cmd.Parameters.AddWithValue( "@Status" , c.Status); // Connection open here conn.Open(); int rows = cmd.ExecuteNonQuery(); // If the query runs succesfully then the value of rows will be > 0 else its value will be 0 if (rows > 0) { isSuccess = true ; } else { isSuccess = false ; } } finally { // close connection conn.Close(); } return isSuccess; } // Method to update data in database from our application public bool Update(ContactClass c) { // Create a default returntype and set its default value to false bool isSuccess = false ; SqlConnection conn = new SqlConnection(myconnstrng); try { // SQL to update data in the database string sql = "UPDATE tbl_contact SET FirstName=@FirstName, LastName=@LastName, Phone=@Phone, Email=@Email, Note=@Note, Status=@Status WHERE ContactID=@ContactID" ; // Creating sql command SqlCommand cmd = new SqlCommand(sql, conn); // Create Parameteres to add value cmd.Parameters.AddWithValue( "@FirstName" , c.FirstName); cmd.Parameters.AddWithValue( "@LastName" , c.LastName); cmd.Parameters.AddWithValue( "@Phone" , c.Phone); cmd.Parameters.AddWithValue( "@Email" , c.Email); cmd.Parameters.AddWithValue( "@Note" , c.Note); cmd.Parameters.AddWithValue( "@Status" , c.Status); cmd.Parameters.AddWithValue( "@ContactID" , c.ContactID); // Open database connection conn.Open(); int rows = cmd.ExecuteNonQuery(); // If the query rund succesfully then the value of rows will be > 0 else its value will be 0 if (rows > 0) { isSuccess = true ; } else { isSuccess = false ; } } catch (Exception ex) { } finally { } return isSuccess; } // Method to delete data from database public bool Delete(ContactClass c) { // Create a default return value and set its value to false bool isSuccess = false ; // Create SQL Connection SqlConnection conn = new SqlConnection(myconnstrng); try { // SQL to delete data string sql = "DELETE FROM tbl_contact WHERE ContactID=@ContactID" ; // Creating SQL command SqlCommand cmd = new SqlCommand(sql, conn); cmd.Parameters.AddWithValue( "@ContactID" , c.ContactID); // Open SQL connection conn.Open(); int rows = cmd.ExecuteNonQuery(); // If the query run succesfully then the value of rows is > 0 else its value is 0 if (rows > 0) { isSuccess = true ; } else { isSuccess = false ; } } catch (Exception ex) { } finally { // Close database connection conn.Close(); } return isSuccess; } } } RContact.java namespace Rcontact { public partial class Rcontact : Form { public Rcontact() { InitializeComponent(); } // gets the errrors how to fix it and why are they there? ContactClass c = new ContactClass(); private void ComboBox1_SelectedIndexChanged(object sender, EventArgs e) { } private void Label6_Click(object sender, EventArgs e) { } private void BtnAdd_Click(object sender, EventArgs e) { // Get the value from the input fields c.FirstName = tbFirstName.Text; c.LastName = tbLastName.Text; c.Phone = tbPhone.Text; c.Email = tbEmail.Text; c.Note = tbNote.Text; c.Status = tbNote.Text; // Inserting data into database using method created in step 3 bool succes = c.Insert(c); if (succes == true ) { // Succesfolly inserted MessageBox.Show( "Now contact succesfully inserted" ); } else { // faild to add contact MessageBox.Show( "Failed to add new contact. Try again. " ); } } } }