dev-notes/docs/languages/dotnet/database/ado.net.md

ADO.NET

ADO.NET is a set of classes that expose data access services for .NET. The ADO.NET classes are found in System.Data.dll, and are integrated with the XML classes found in System.Xml.dll.

ADO.NET provider for SQLite

Connection Strings

SQL Server 2019

• Standard Security:
  • Server=<server_name>; Database=<database>; UID=<user>; Pwd=<password>;
  • Server=<server_name>; Database=<database>; User ID=<user>; Password=<password>;
  • Data Source=<server_name>; Initial Catalog=<database>; UID=<user>; Pwd=<password>;
• Specific Instance: Server=<server_name>\<instance_name>; Database=<database>; User ID=<user>; Password=<password>;
• Trusted Connection (WinAuth): Server=<server_name>; Database=<database>; Trusted_Connection=True;
• MARS: Server=<server_name>; Database=<database>; Trusted_Connection=True; MultipleActiveResultSets=True;

Note

: Multiple Active Result Sets (MARS) is a feature that works with SQL Server to allow the execution of multiple batches on a single connection.

SQLite

• Basic: Data Source: path\to\db.sqlite3; Version=3;
• In-Memory Database: Data Source=:memory:; Version=3; New=True
• With Password: Data Source: path\to\db.sqlite3; Version=3; Password=<password>

Connection to DB

using System;
using System.Data.SqlClient;  // ADO.NET Provider, installed through NuGet

namespace <namespace>
{
    class Program
    {
        static void Main(string[] args)
        {
            // Connection to SQL Server DBMS
            SqlConnectionStringBuilder connectionString = new SqlConnectionStringBuilder();
            connectionString.DataSource = "<server_name>";
            connectionString.UserID = "<user>";
            connectionString.Password = "<password>";
            connectionString.InitialCatalog = "<database>";

            // more compact
            SqlConnectionStringBuilder connectionString = new SqlConnectionStringBuilder("Server=<server_name>;Database=<database>;UID=<user>;Pwd=<password>")
        }
    }
}

DB Interrogation

SqlConnection

using (SqlConnection connection = new SqlConnection())
{
    connection.ConnectionString = connectionString.ConnectionString;
    connection.Open();  // start communication w/ sql server
}

// more compact
using (SqlConnection connection = new SqlConnection(connectionString)) {
    connection.Open()
}

SqlCommand

string sql = "<sql_instruction>";

using (SqlCommand command = new SqlCommand())
{
    command.Connection = connection;  // SqlConnection
    command.CommandText = "... @Parameter";  // or name of StoredProcedure

    // add parameters to the SqlParameterCollection, WARNING: table names or columns cannot be parameters
    command.Parameters.Add("@Parameter", SqlDbType.<DBType>, columnLength).Value = value;
    command.Parameters.AddWithValue("@Parameter", value);
    command.Parameters.AddWithValue("@Parameter", (object) value ?? DBNull.Value);  // if Parameter is nullable

    // Create an instance of a SqlParameter object.
    command.CreateParameter();

    command.CommandType = CommandType.Text;  // or StoredProcedure

    int affectedRows = command.ExecuteNonQuery();  // execute the query and return the number of affected rows
}

SqlDataReader

using (SqlDataReader cursor = command.ExecuteReader())  // object to get data from db
{
    while (cursor.Read())  // get data till possible
    {
        // preferred methodology
        cursor["<column_name>"].ToString();  // retrieve data form the column
        cursor[<column_index>].ToString();  // retrieve data form the column

        // check for null before retrieving the value
        if(!cursor.IsDBNull(n))
        {
            cursor.Get<SystemType>(index);  // retrieve data form the n-th column
        }
    }
}