best solution for multiple insert update solution - npgsql

Question

Struggle with understanding C# & Npgsql as a beginner. Following code examples:
// Insert some data
using (var cmd = new NpgsqlCommand())
{ cmd.Connection = conn;
cmd.CommandText = "INSERT INTO data (some_field) VALUES (#p)";
cmd.Parameters.AddWithValue("p", "Hello world");
cmd.ExecuteNonQuery();
}
The syntax for more than one insert & update statement like this is clear so far:
cmd.CommandText = "INSERT INTO data (some_field) VALUES (#p);INSERT INTO data1...;INSERT into data2... and so on";
But what is the right solution for a loop which should handle one statement within.
This works not:
// Insert some data
using (var cmd = new NpgsqlCommand())
{
foreach(s in SomeStringCollectionOrWhatever)
{
cmd.Connection = conn;
cmd.CommandText = "INSERT INTO data (some_field) VALUES (#p)";
cmd.Parameters.AddWithValue("p", s);
cmd.ExecuteNonQuery();
}
}
It seems the values will be "concatenated" or remembered. I cannot see any possibility to "clear" the existing cmd-object.
My second solution would be to wrap the whole "using" block into the loop. But every cycle would create a new object. That seems ugly to me.
So what is the best solution for my problem?

Answer 1

To insert lots of rows efficiently, take a look at Npgsql's bulk copy feature - the API is more suitable (and more efficient) for inserting large numbers of rows than concatenating INSERT statements into a batch like you're trying to do.

Answer 2

If you want to rerun the same SQL with changing parameter values, you can do the following:
using (var cmd = new NpgsqlCommand("INSERT INTO data (some_field) VALUES (#p)", conn))
{
var p = new NpgsqlParameter("p", DbType.String); // Adjust DbType according to type
cmd.Parameters.Add(p);
cmd.Prepare(); // This is optional but will optimize the statement for repeated use
foreach(var s in SomeStringCollectionOrWhatever)
{
p.Value = s;
cmd.ExecuteNonQuery();
}
}

Answer 3

If you need lots of rows and performance is key then i would recommend Npgsql's bulk copy capability as #Shay mentioned. But if you are looking for quick way to do this without the bulk copy i would recommend to use Dapper.
Consider the example below.
Lets say you have a class called Event and a list of events to add.
List<Event> eventsToInsert = new List<Event>
{
new Event() { EventId = 1, EventName = "Bday1" },
new Event() { EventId = 2, EventName = "Bday2" },
new Event() { EventId = 3, EventName = "Bday3" }
};
The snippet that would add the list to the DB shown below.
var sqlInsert = "Insert into events( eventid, eventname ) values (#EventId, #EventName)";
using (IDbConnection conn = new NpgsqlConnection(cs))
{
conn.Open();
// Execute is an extension method supplied by Dapper
// This code will add all the entries in the eventsToInsert List and match up the values based on property name. Only caveat is that the property names of the POCO should match the placeholder names in the SQL Statement.
conn.Execute(sqlInsert, eventsToInsert);
// If we want to retrieve the data back into the list
List<Event> eventsAdded;
// This Dapper extension will return an Ienumerable, so i cast it to a List.
eventsAdded = conn.Query<Event>("Select * from events").ToList();
foreach( var row in eventsAdded)
{
Console.WriteLine($"{row.EventId} {row.EventName} was added");
}
}
-HTH