Support DESC-flag in migrations and scaffolding (#126)

Author: la-we

src/FirebirdSql.EntityFrameworkCore.Firebird/Migrations/FbMigrationsSqlGenerator.cs

@@ -201,6 +201,19 @@ protected override void Generate(CreateIndexOperation operation, IModel model, M
 		{
 			builder.Append("UNIQUE ");
 		}
+
+		if (operation.IsDescending is not null && operation.IsDescending.Length > 0)
+		{
+			var isDescending = operation.IsDescending[0];
+			if (operation.IsDescending.Any(x => x != isDescending))
+				throw new NotSupportedException("Mixed order indices are not supported by Firebird.");
+
+			if (isDescending)
+			{
+				builder.Append("DESC ");
+			}
+		}
+
 		IndexTraits(operation, model, builder);
 		builder.Append("INDEX ");
 		builder.Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Name));

src/FirebirdSql.EntityFrameworkCore.Firebird/Scaffolding/Internal/FbDatabaseModelFactory.cs

@@ -311,6 +311,7 @@ private void GetPrimaryKeys(DbConnection connection, IReadOnlyList<DatabaseTable
 		@"SELECT
                trim(I.rdb$index_name) as INDEX_NAME,
                COALESCE(I.rdb$unique_flag, 0) as IS_UNIQUE,
+               Coalesce(I.rdb$index_type, 0) = 1 as IS_DESC,
                list(trim(sg.RDB$FIELD_NAME)) as COLUMNS
               FROM
                RDB$INDICES i
@@ -319,7 +320,7 @@ private void GetPrimaryKeys(DbConnection connection, IReadOnlyList<DatabaseTable
               WHERE
                trim(i.rdb$relation_name) = '{0}'
               GROUP BY
-               INDEX_NAME, IS_UNIQUE ;";
+               INDEX_NAME, IS_UNIQUE, IS_DESC ;";
 
 	/// <remarks>
 	/// Primary keys are handled as in <see cref="GetConstraints"/>, not here
@@ -343,11 +344,18 @@ private void GetIndexes(DbConnection connection, IReadOnlyList<DatabaseTable> ta
 							IsUnique = reader.GetBoolean(1),
 						};
 
-						foreach (var column in reader.GetString(2).Split(','))
+						foreach (var column in reader.GetString(3).Split(','))
 						{
 							index.Columns.Add(table.Columns.Single(y => y.Name == column.Trim()));
 						}
 
+						if (reader.GetBoolean(2))
+						{
+							var isDescending = new bool[index.Columns.Count];
+							isDescending.AsSpan().Fill(true);
+							index.IsDescending = isDescending;
+						}
+
 						table.Indexes.Add(index);
 					}
 				}