sqlite-utils duplicate command, closes #454, refs #449

Also made it so .duplicate() raises new NoTable exception rather than raising
an AssertionError if the source table does not exist.

docs/cli-reference.rst

@@ -1176,6 +1176,20 @@ reset-counts
       -h, --help             Show this message and exit.
 
 
+duplicate
+=========
+
+::
+
+    Usage: sqlite-utils duplicate [OPTIONS] PATH TABLE NEW_TABLE
+
+      Create a duplicate of this table, copying across the schema and all row data.
+
+    Options:
+      --load-extension TEXT  SQLite extensions to load
+      -h, --help             Show this message and exit.
+
+
 drop-table
 ==========
 

docs/cli.rst

@@ -1476,6 +1476,15 @@ You can specify foreign key relationships between the tables you are creating us
 
 If a table with the same name already exists, you will get an error. You can choose to silently ignore this error with ``--ignore``, or you can replace the existing table with a new, empty table using ``--replace``.
 
+.. _cli_duplicate_table:
+
+Duplicating tables
+==================
+
+The ``duplicate`` command duplicates a table - creating a new table with the same schema and a copy of all of the rows::
+
+    $ sqlite-utils duplicate books.db authors authors_copy
+
 .. _cli_drop_table:
 
 Dropping tables

docs/python-api.rst

@@ -691,6 +691,8 @@ The ``table.duplicate()`` method creates a copy of the table, copying both the t
 
 The new ``authors_copy`` table will now contain a duplicate copy of the data from ``authors``.
 
+This method raises ``sqlite_utils.db.NoTable`` if the table does not exist.
+
 .. _python_api_bulk_inserts:
 
 Bulk inserts

sqlite_utils/cli.py

@@ -5,7 +5,7 @@ from datetime import datetime
 import hashlib
 import pathlib
 import sqlite_utils
-from sqlite_utils.db import AlterError, BadMultiValues, DescIndex
+from sqlite_utils.db import AlterError, BadMultiValues, DescIndex, NoTable
 from sqlite_utils.utils import maximize_csv_field_size_limit
 from sqlite_utils import recipes
 import textwrap
@@ -1465,6 +1465,27 @@ def create_table(
     )
 
 
+@cli.command(name="duplicate")
+@click.argument(
+    "path",
+    type=click.Path(file_okay=True, dir_okay=False, allow_dash=False),
+    required=True,
+)
+@click.argument("table")
+@click.argument("new_table")
+@load_extension_option
+def create_table(path, table, new_table, load_extension):
+    """
+    Create a duplicate of this table, copying across the schema and all row data.
+    """
+    db = sqlite_utils.Database(path)
+    _load_extensions(db, load_extension)
+    try:
+        db[table].duplicate(new_table)
+    except NoTable:
+        raise click.ClickException('Table "{}" does not exist'.format(table))
+
+
 @cli.command(name="drop-table")
 @click.argument(
     "path",

sqlite_utils/db.py

@@ -1,3 +1,4 @@
+from ast import Not
 from .utils import (
     chunks,
     hash_record,
@@ -224,6 +225,11 @@ class NoObviousTable(Exception):
     pass
 
 
+class NoTable(Exception):
+    "Specified table does not exist"
+    pass
+
+
 class BadPrimaryKey(Exception):
     "Table does not have a single obvious primary key"
     pass
@@ -1482,7 +1488,8 @@ class Table(Queryable):
 
         :param new_name: Name of the new table
         """
-        assert self.exists()
+        if not self.exists():
+            raise NoTable(f"Table {self.name} does not exist")
         with self.db.conn:
             sql = "CREATE TABLE [{new_table}] AS SELECT * FROM [{table}];".format(
                 new_table=new_name,

tests/test_cli.py

@@ -2129,3 +2129,26 @@ def test_analyze(tmpdir, options, expected):
     result = CliRunner().invoke(cli.cli, ["analyze", db_path] + options)
     assert result.exit_code == 0
     assert list(db["sqlite_stat1"].rows) == expected
+
+
+def test_duplicate_table(tmpdir):
+    db_path = str(tmpdir / "test.db")
+    db = Database(db_path)
+    db["one"].insert({"id": 1, "name": "Cleo"}, pk="id")
+    # First try a non-existent table
+    result_error = CliRunner().invoke(
+        cli.cli,
+        ["duplicate", db_path, "missing", "two"],
+        catch_exceptions=False,
+    )
+    assert result_error.exit_code == 1
+    assert result_error.output == 'Error: Table "missing" does not exist\n'
+    # Now try for a table that exists
+    result = CliRunner().invoke(
+        cli.cli,
+        ["duplicate", db_path, "one", "two"],
+        catch_exceptions=False,
+    )
+    assert result.exit_code == 0
+    assert db["one"].columns_dict == db["two"].columns_dict
+    assert list(db["one"].rows) == list(db["two"].rows)

tests/test_duplicate.py

@@ -1,3 +1,4 @@
+from sqlite_utils.db import NoTable
 import datetime
 import pytest
 
@@ -38,5 +39,5 @@ def test_duplicate(fresh_db):
 
 
 def test_duplicate_fails_if_table_does_not_exist(fresh_db):
-    with pytest.raises(AssertionError):
+    with pytest.raises(NoTable):
         fresh_db["not_a_table"].duplicate("duplicated")