Add LoadData from DB functionality

LoggingClient/LoggingClient/Repository/CustomerRepository.cs

@@ -1,5 +1,8 @@
 using LoggingClient.Model;
+using MySql.Data.MySqlClient;
+using System;
 using System.Collections.Generic;
+using System.Windows;
 
 namespace LoggingClient.Repository
 {
@@ -7,16 +10,19 @@ namespace LoggingClient.Repository
     {
         public CustomerRepository(string connectionString) : base(connectionString)
         {
-
+            Customers = new List<Customer>();
         }
 
-        public override string TableName => throw new System.NotImplementedException();
+        public override string TableName => "customer";
 
-        public override string ColumnsForSelect => throw new System.NotImplementedException();
+        public override string ColumnsForSelect => "customer_id, firstname, lastname, customernumber, kundenkonto_fk, tel, email, url, password";
 
-        public override string ColumnsForAdd => throw new System.NotImplementedException();
+        public override string ColumnsForAdd => "firstname, lastname, customernumber, kundenkonto_fk, tel, email, url, password";
 
-        public override string PrimaryKeyFromTable => throw new System.NotImplementedException();
+        public override string PrimaryKeyFromTable => "customer_id";
+
+        public List<Customer> Customers { get; set; }
+        public Customer _Customers { get; set; }
 
         public override void Add(Customer entity)
         {
@@ -40,7 +46,37 @@ namespace LoggingClient.Repository
 
         public override List<Customer> GetAll()
         {
-            throw new System.NotImplementedException();
+            try
+            {
+                using (var conn = new MySqlConnection(ConnectionString))
+                {
+                    conn.Open();
+                    using (MySqlCommand cmd = conn.CreateCommand())
+                    {
+                        cmd.CommandText = $"SELECT {ColumnsForSelect} FROM {TableName}";
+                        var reader = cmd.ExecuteReader();
+                        while (reader.Read())
+                        {
+                            Customers.Add(new Customer(
+                                reader.GetInt32("customer_id"),
+                                reader.GetValue(reader.GetOrdinal("firstname")) as string,
+                                reader.GetValue(reader.GetOrdinal("lastname")) as string,
+                                reader.GetValue(reader.GetOrdinal("customernumber")) as string,
+                                reader.GetInt32("kundenkonto_fk"),
+                                reader.GetValue(reader.GetOrdinal("tel")) as string,
+                                reader.GetValue(reader.GetOrdinal("email")) as string,
+                                reader.GetValue(reader.GetOrdinal("url")) as string,
+                                reader.GetValue(reader.GetOrdinal("password")) as string
+                            ));
+                        }
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                MessageBox.Show("Error occurred: " + ex.Message);
+            }
+            return Customers;
         }
 
         public override Customer GetSingle<P>(P pkValue)