C#•17mo ago

✅ Issues with setting up different classes and sql connection

Could someone help me understand how I can setup this SQL connection? it's my first time organizing my code into different folders and really structuring my app with different folders, etc. I get the error "A field initializer cannot reference the non-static field, method or property 'Customer.connection' ". I want to make it so that I have a connection class that handles the connection. Currently I have: model class that talks to the dal class that talks to the connection class I have the following class:

    public class Customer : ICustomer
    {
        private Connection connection;
        CustomerDAO db = new CustomerDAO(connection.CreateConnection());
        public int Id { get; set; }
        public string Name { get; set; }
        public string Email { get; set; }
        public string Phone { get; set; }
        public string Address { get; set; }

        // ctor
        public Customer(....)
        {
            .........
        }

        public void Create(Customer customer)
        {
            db.Create(customer)
        }

    public class Customer : ICustomer
    {
        private Connection connection;
        CustomerDAO db = new CustomerDAO(connection.CreateConnection());
        public int Id { get; set; }
        public string Name { get; set; }
        public string Email { get; set; }
        public string Phone { get; set; }
        public string Address { get; set; }

        // ctor
        public Customer(....)
        {
            .........
        }

        public void Create(Customer customer)
        {
            db.Create(customer)
        }

My connection class looks like this

    public class Connection
    {
        private string connectionString = "example string";

        public SqlConnection CreateConnection()
        {
            SqlConnection connection = new SqlConnection(connectionString);
            return connection;
        }
    }

    public class Connection
    {
        private string connectionString = "example string";

        public SqlConnection CreateConnection()
        {
            SqlConnection connection = new SqlConnection(connectionString);
            return connection;
        }
    }

19 Replies

Jimmacle•17mo ago

the problem is

        CustomerDAO db = new CustomerDAO(connection.CreateConnection());

        CustomerDAO db = new CustomerDAO(connection.CreateConnection());

you can't access connection in a field initializer because it's not guaranteed to be initialized at that point. you can assign db in the constructor body instead it looks like the real issue is that the whole Connection class should be static - it doesn't contain any state and it doesn't make sense to ever have an instance of it

kevinOP•17mo ago

would i make the entire class static or just the connectionstring ?

Jimmacle•17mo ago

the whole class, then you don't need a Connection connection; field you can simply call Connection.CreateConnection() i'm also suspicious why your model needs to contain a database connection, but one thing at a time

kevinOP•17mo ago

Currently I get alot of errors in my customerDAO class here's the code

public class CustomerDAO
    {
        private Connection connection;

        public CustomerDAO(Connection connection)
        {
            this.connection = connection;
        }

        #region Create
        public void Create(Customer customer)
        {
            using (SqlConnection sqlConnection = connection.CreateConnection())
            {
                sqlConnection.Open();
                string query = "INSERT INTO Customer (Name, Email, Phone, Address) VALUES (@Name, @Email, @Phone, @Address)";
                SqlCommand command = new SqlCommand(query, sqlConnection);
                command.Parameters.AddWithValue("@Name", customer.Name);
                command.Parameters.AddWithValue("@Email", customer.Email);
                command.Parameters.AddWithValue("@Phone", customer.Phone);
                command.Parameters.AddWithValue("@Address", customer.Address);
                command.ExecuteNonQuery();
            }
        }
        #endregion

public class CustomerDAO
    {
        private Connection connection;

        public CustomerDAO(Connection connection)
        {
            this.connection = connection;
        }

        #region Create
        public void Create(Customer customer)
        {
            using (SqlConnection sqlConnection = connection.CreateConnection())
            {
                sqlConnection.Open();
                string query = "INSERT INTO Customer (Name, Email, Phone, Address) VALUES (@Name, @Email, @Phone, @Address)";
                SqlCommand command = new SqlCommand(query, sqlConnection);
                command.Parameters.AddWithValue("@Name", customer.Name);
                command.Parameters.AddWithValue("@Email", customer.Email);
                command.Parameters.AddWithValue("@Phone", customer.Phone);
                command.Parameters.AddWithValue("@Address", customer.Address);
                command.ExecuteNonQuery();
            }
        }
        #endregion

kevinOP•17mo ago

Jimmacle•17mo ago

when you make a class static you have to make all its members static too and you can no longer have variables of that type because there is nothing to store

kevinOP•17mo ago

    public static class Connection
    {
        private static string connectionString = "example string";

        public static SqlConnection CreateConnection()
        {
            SqlConnection connection = new SqlConnection(connectionString);
            return connection;
        }
    }

    public static class Connection
    {
        private static string connectionString = "example string";

        public static SqlConnection CreateConnection()
        {
            SqlConnection connection = new SqlConnection(connectionString);
            return connection;
        }
    }

Wait so I would remove the connectionString then like this

    public static class Connection
    {
        public static SqlConnection CreateConnection()
        {
            SqlConnection connection = new SqlConnection("example string");
            return connection;
        }
    }

    public static class Connection
    {
        public static SqlConnection CreateConnection()
        {
            SqlConnection connection = new SqlConnection("example string");
            return connection;
        }
    }

Jimmacle•17mo ago

no, your first one was fine what errors do you have left?

kevinOP•17mo ago

MODiX•17mo ago

Jimmacle

and you can no longer have variables of that type because there is nothing to store

Quoted by

<@901546879530172498> from #Issues with setting up different classes and sql connection (click here)

React with ❌ to remove this embed.

kevinOP•17mo ago

How would i use the connection now ?

Jimmacle•17mo ago

by calling it directly on the type name

kevinOP•17mo ago

currently doing it like this using (SqlConnection sqlConnection = connection.CreateConnection())

Jimmacle•17mo ago

Connection.CreateConnection() you don't need any connection variables anymore

kevinOP•17mo ago

Ah okay, it works now, thanks Wondering though and correct me if im wrong but isnt making it static unsafe because im storing my sql connection string in there ? any object could access the sql connection or am i wrong ?

Jimmacle•17mo ago

no, because it's private frankly storing your connection string anywhere in your source code is unsafe, normally you load it from somewhere else like a config file

kevinOP•17mo ago

This is for a school project so I’m not really worried about safety that much just wondering Usually i would store it somewhere in .env right ?

Jimmacle•17mo ago

environment variables are one option back to this, static on a class just controls whether a class can have instances of itself or not - it doesn't affect accessibility of its members so it's no less safe than it already was the main thing is that it's bad to use static classes for anything that stores information that can change over your program's execution, it tends to make things messy and harder to debug

Accord•17mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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✅ Issues with setting up different classes and sql connection