Update database handling code (#247)

web/backend/Database/Database.Connection/DefaultSqlConnectionFactory.cs

@@ -0,0 +1,46 @@
+using System.Data.Common;
+using Microsoft.Data.SqlClient;
+using Microsoft.Extensions.Configuration;
+
+namespace Database.Connection;
+
+/// <summary>
+///     Default <see cref="DefaultSqlConnectionFactory" /> implementation that creates SQL Server connections,
+///     resolving the connection string from environment variables or application configuration.
+/// </summary>
+public class DefaultSqlConnectionFactory(IConfiguration configuration) : ISqlConnectionFactory
+{
+    /// <summary>
+    ///     The resolved SQL Server connection string, preferring (in order): the <c>DB_CONNECTION_STRING</c>
+    ///     configuration value, and a connection string built from individual <c>DB_*</c> configuration values.
+    /// </summary>
+    /// <exception cref="InvalidOperationException">Thrown when no connection string can be resolved from any source.</exception>
+    public string ConnectionString
+    {
+        get
+        {
+            string? fullConnectionString = configuration["DB_CONNECTION_STRING"];
+            if (!string.IsNullOrEmpty(fullConnectionString))
+                return fullConnectionString;
+
+            // Try to build from individual configuration values (preferred method for Docker)
+            if (
+                SqlConnectionStringHelper.TryGetStandardDbConnectionString(
+                    configuration,
+                    out var connectionString
+                )
+            )
+                return connectionString;
+
+            throw new InvalidOperationException(
+                "Database connection string not configured. Set DB_CONNECTION_STRING or DB_SERVER, DB_NAME, DB_USER, DB_PASSWORD env vars."
+            );
+        }
+    }
+
+    /// <inheritdoc />
+    public SqlConnection CreateConnection()
+    {
+        return new SqlConnection(ConnectionString);
+    }
+}