`table.xindexes` using `PRAGMA index_xinfo(table)`

[simonw]

PRAGMA index_xinfo(table) DOES return that data:

(Pdb) [c[0] for c in fresh_db.execute("PRAGMA > index_xinfo('idx_dogs_age_name')").description]
['seqno', 'cid', 'name', 'desc', 'coll', 'key']
(Pdb) fresh_db.execute("PRAGMA index_xinfo('idx_dogs_age_name')").fetchall()
[(0, 2, 'age', 1, 'BINARY', 1), (1, 0, 'name', 0, 'BINARY', 1), (2, -1, None, 0, 'BINARY', 0)]

See https://sqlite.org/pragma.html#pragma_index_xinfo

Example output: https://covid-19.datasettes.com/covid?sql=select+*+from+pragma_index_xinfo%28%27idx_ny_times_us_counties_date%27%29
Originally posted by @simonw in #260 (comment)

[simonw]

This would be a breaking change - and the fact that it returns auxiliary columns isn't particularly useful for most cases - "Auxiliary columns are additional columns needed to locate the table entry that corresponds to each index entry".

Instead, I'm going to add a new property table.xindexes which exposes this.

[simonw]

In prototyping this out I realize that I actually want to get back the name of each index, then for each of them the detailed list of index columns. Here's the test from my initial prototype:

def test_xindexes(fresh_db):
    fresh_db.executescript(
        """
        create table Gosh (c1 text, c2 text, c3 text);
        create index Gosh_c1 on Gosh(c1);
        create index Gosh_c2c3 on Gosh(c2, c3 desc);
    """
    )
    assert fresh_db["Gosh"].xindexes == [
        (
            "Gosh_c2c3",
            [
                XIndex(seqno=0, cid=1, name="c2", desc=0, coll="BINARY", key=1),
                XIndex(seqno=1, cid=2, name="c3", desc=1, coll="BINARY", key=1),
                XIndex(seqno=2, cid=-1, name=None, desc=0, coll="BINARY", key=0),
            ],
        ),
        (
            "Gosh_c1",
            [
                XIndex(seqno=0, cid=0, name="c1", desc=0, coll="BINARY", key=1),
                XIndex(seqno=1, cid=-1, name=None, desc=0, coll="BINARY", key=0),
            ],
        ),
    ]

[simonw]

I'm going to return XIndex(name, columns) - where columns is a list of XIndexColumn.

[simonw]

New design:

def test_xindexes(fresh_db):
    fresh_db.executescript(
        """
        create table Gosh (c1 text, c2 text, c3 text);
        create index Gosh_c1 on Gosh(c1);
        create index Gosh_c2c3 on Gosh(c2, c3 desc);
    """
    )
    assert fresh_db["Gosh"].xindexes == [
        XIndex(
            name="Gosh_c2c3",
            columns=[
                XIndexColumn(seqno=0, cid=1, name="c2", desc=0, coll="BINARY", key=1),
                XIndexColumn(seqno=1, cid=2, name="c3", desc=1, coll="BINARY", key=1),
                XIndexColumn(seqno=2, cid=-1, name=None, desc=0, coll="BINARY", key=0),
            ],
        ),
        XIndex(
            name="Gosh_c1",
            columns=[
                XIndexColumn(seqno=0, cid=0, name="c1", desc=0, coll="BINARY", key=1),
                XIndexColumn(seqno=1, cid=-1, name=None, desc=0, coll="BINARY", key=0),
            ],
        ),
    ]

[simonw]

Documentation: https://sqlite-utils.datasette.io/en/latest/python-api.html#xindexes