I have methods to get data from database as below. The problem is if I have a number of classes, I need to write a number of get-data methods to retrieve the list of corresponding objects although the the logic is the same, only the classes, properties and table name are different.
I want to know if it is possible to write only 1 method to use for all classes. The challenge part is I don't know to how to cast the reader data to the data type of the properties.
I will pass in the object, the columns and the table name. For example:
// I want to write this method so it can be used for all classes
public List<Object> getData(string className, string[] columns, string tableName) {...}
public List<Client> GetClients()
{
List<Client> list = new List<Client>();
try
{
conn.Open();
string sql = "SELECT id, clientName, info, hidden from clients";
MySqlCommand cmd = new MySqlCommand(sql, conn);
MySqlDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
Client p = new Client((int)rdr[0], (string)rdr[1], (string)rdr[2], Convert.ToBoolean(rdr["hidden"]));
list.Add(p);
}
rdr.Close();
return list;
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
return null;
}
finally
{
conn.Close();
}
}
public List<RepPrefix> GetRepPrefixes()
{
List<RepPrefix> list = new List<RepPrefix>();
try
{
conn.Open();
string sql = "SELECT id, prefixName, hidden from repPrefix";
MySqlCommand cmd = new MySqlCommand(sql, conn);
MySqlDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
RepPrefix p = new RepPrefix((int)rdr[0], (string)rdr[1], Convert.ToBoolean(rdr["hidden"]));
list.Add(p);
}
rdr.Close();
return list;
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
return null;
}
finally
{
conn.Close();
}
}
CodePudding user response：
If your Client and RepPrefix have settable properties with names that match the database columns, you can avoid the need to write a lot of boilerplate code by using a library like Dapper:
var clients = conn.Query<Client>("SELECT id, clientName, info, hidden from clients;").ToList();
var repPrefixes = conn.Query<RepPrefix>("SELECT id, prefixName, hidden from repPrefix;").ToList();
// ...
class Client
{
public int Id { get; set; }
public string ClientName { get; set; }
public string Info { get; set; }
public bool Hidden { get; set; }
}
It will map from DB column names to C# property names, perform the appropriate type conversions, etc.
If you don't want to use an external library, but want to write the code yourself, I would modify the signature of getData to take a function that takes a DbDataReader and returns an initialized object of type T:
// method that executes the query and invokes a callback to read the data
public List<T> getData<T>(string[] columns, string tableName, Func<DbDataReader, T> readData)
{
var list = new List<T>();
try
{
conn.Open();
string sql = "SELECT " string.Join(",", columns) " from " tableName;
using var cmd = new MySqlCommand(sql, conn);
using var rdr = cmd.ExecuteReader();
while (rdr.Read())
{
// read the data from this row and construct a new T
T t = readData(rdr);
list.Add(p);
}
return list;
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
return null;
}
finally
{
conn.Close();
}
}
// an example of calling getData with a custom callback that creates Client objects
List<Client> GetClients() =>
getData(new[] { "id", "clientName", "info", "hidden" }, "clients",
rdr => new Client(rdr.GetInt32(0), rdr.GetString(1), rdr.GetString(2), rdr.GetBoolean(3)));
CodePudding user response：
Here is you generic method
- Create a
DatabaseExtensions.csclass and make it static. Paste below code inside class.
public static MySqlDataReader Query(this MySqlConnection connection, string SQLQuery, Action<MySqlDataReader> datareader)
{
//automatically close connection after use
using (connection)
{
connection.Open();
using (MySqlCommand command = new MySqlCommand(SQLQuery, connection))
using (MySqlDataReader reader = command.ExecuteReader())
{
// here you can pass the reader,
// you are still inside the using block
while (reader.Read())
datareader.Invoke(reader);
}
}
return default;
}
- In your caller code
///section for client start
public List<Client> GetClients()
{
List<Client> list = new List<Client>();
// hope you have a connection like var connection = new MySqlConnection();
connection.Query("SELECT id, clientName, info, hidden from clients", ReadFromReader);
void ReadFromReader(MySqlDataReader reader)
{
Client p = new Client((int)rdr[0], (string)rdr[1], (string)rdr[2], Convert.ToBoolean(rdr["hidden"]));
list.Add(p);
}
return clients;
}
//section for client end
// section for RepPrefix start
public List<Client> GetRepPrefixes()
{
List<RepPrefix> list = new List<RepPrefix>();
// hope you have a connection like var connection = new MySqlConnection();
connection.Query("SELECT id, prefixName, hidden from repPrefix", ReadFromReader);
void ReadFromReader(MySqlDataReader reader)
{
RepPrefix p = new RepPrefix((int)rdr[0], (string)rdr[1], Convert.ToBoolean(rdr["hidden"]));
list.Add(p);
}
return list;
}
//section for RepPrefix end
CodePudding user response：
First, I highly recommend Dapper. Dapper will map objects to SQL statements for you and is performant.
If you have classes that align with your db tables, you could use reflection or some function on each class to generate SELECT, INSERT, and UPDATE statements and then use those same objects as your parameters into the Dapper functions.
CodePudding user response：
Yes, it is possible to write a single method that can be used for all classes with a MySqlConnection in C#.
To do this, you will need to use reflection to dynamically create an instance of the desired class, and then use the Activator.CreateInstance() method to instantiate an object of that type. You can then use the Type.GetProperty() method to access the properties of the class and set their values based on the data from the MySqlDataReader.
Here is an example of how this could be done:
// This method uses reflection to dynamically create an instance of the specified class
// and then sets the values of its properties based on the data from the MySqlDataReader
public List<object> GetData(string className, string[] columns, string tableName)
{
// Create a list to hold the objects
List<object> list = new List<object>();
try
{
conn.Open();
// Create the SQL query string
string sql = "SELECT " string.Join(", ", columns) " FROM " tableName;
MySqlCommand cmd = new MySqlCommand(sql, conn);
MySqlDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
// Use reflection to dynamically create an instance of the specified class
Type t = Type.GetType(className);
object obj = Activator.CreateInstance(t);
// Loop through the columns and set the values of the object's properties
for (int i = 0; i < columns.Length; i )
{
// Use the Type.GetProperty() method to access the property with the specified name
PropertyInfo prop = t.GetProperty(columns[i]);
// Set the value of the property using the data from the MySqlDataReader
prop.SetValue(obj, rdr[i]);
}
// Add the object to the list
list.Add(obj);
}
rdr.Close();
return list;
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
return null;
}
finally
{
conn.Close();
}
}
You can then call this method like this:
// Get the list of clients
List<object> clients = GetData("Client", new string[] {"id", "clientName", "info", "hidden"}, "clients");
// Get the list of rep prefixes
List<object> repPrefixes = GetData("RepPrefix", new string[] {"id", "prefixName", "hidden"}, "repPrefix");
Keep in mind that this method will return a list of objects of the specified type, so you will need to cast the objects to the appropriate type when using them. For example:
// Cast the objects to the Client type and use them
foreach (Client client in clients)
{
Console.WriteLine(client.clientName);
}