Various fixes:

* Functions for finding one or multiple entries, with internal
  pagination.
* Limit engine pool size to 1
* Don't block connections.

sqlaload/__init__.py

@@ -4,5 +4,5 @@ from sqlaload.schema import create_table, load_table, get_table
 from sqlaload.schema import create_column
 from sqlaload.write import add_row, update_row
 from sqlaload.write import upsert, update
-from sqlaload.query import distinct, resultiter, all
+from sqlaload.query import distinct, resultiter, all, find_one, find
 

sqlaload/query.py

@@ -1,6 +1,7 @@
 import logging
+from itertools import count
 
-from sqlalchemy.sql import expression
+from sqlalchemy.sql import expression, and_
 
 log = logging.getLogger(__name__)
 
@@ -14,14 +15,47 @@ def resultiter(rp):
             break
         yield dict(zip(keys, row))
 
+def find_one(engine, table, **kw):
+    res = list(find(engine, table, _limit=1, **kw))
+    if not len(res):
+        return None
+    return res[0]
+
+def find(engine, table, _limit=None, _step=5000, _offset=0, 
+         order_by=None, **kw):
+
+    if order_by is None:
+        order_by = [table.c.id.asc()]
+
+    qargs = []
+    try:
+        for col, val in kw.items():
+            qargs.append(table.c[col]==val)
+    except KeyError:
+        return
+
+    for i in count():
+        qoffset = _offset + (_step * i)
+        qlimit = _step
+        if _limit is not None:
+            qlimit = min(_limit-(_step*i), _step)
+        if qlimit <= 0:
+            break
+        q = table.select(whereclause=and_(*qargs), limit=qlimit,
+                offset=qoffset, order_by=order_by)
+        rows = list(resultiter(engine.execute(q)))
+        if not len(rows):
+            return 
+        for row in rows:
+            yield row
+
 def distinct(engine, table, *columns):
     columns = [table.c[c] for c in columns]
     q = expression.select(columns, distinct=True)
-    return resultiter(engine.execute(q))
+    return list(resultiter(engine.execute(q)))
 
 def all(engine, table):
-    q = table.select()
-    return resultiter(engine.execute(q))
+    return find(engine, table)
 
 
 

sqlaload/schema.py

@@ -1,17 +1,20 @@
 import logging
 from datetime import datetime
+from collections import defaultdict
 
 from sqlalchemy import create_engine
-from sqlalchemy import Integer, UnicodeText, Float, DateTime
+from sqlalchemy import Integer, UnicodeText, Float, DateTime, Boolean
 from sqlalchemy.schema import Table, MetaData, Column
 from sqlalchemy.sql import and_, expression
 from migrate.versioning.util import construct_engine
 
 log = logging.getLogger(__name__)
 
+TABLES = defaultdict(dict)
+
 def connect(url):
     """ Create an engine for the given database URL. """
-    engine = create_engine(url)
+    engine = create_engine(url, pool_size=1)
     engine = construct_engine(engine)
     meta = MetaData()
     meta.bind = engine
@@ -24,20 +27,27 @@ def create_table(engine, table_name):
     col = Column('id', Integer, primary_key=True)
     table.append_column(col)
     table.create(engine)
+    TABLES[engine][table_name] = table
     return table
 
 def load_table(engine, table_name):
     log.debug("Loading table: %s on %r" % (table_name, engine))
-    return Table(table_name, engine._metadata, autoload=True)
+    table = Table(table_name, engine._metadata, autoload=True)
+    TABLES[engine][table_name] = table
+    return table
 
 def get_table(engine, table_name):
+    if table_name in TABLES[engine]:
+        return TABLES[engine][table_name]
     if engine.has_table(table_name):
         return load_table(engine, table_name)
     else:
         return create_table(engine, table_name)
 
 def _guess_type(sample):
-    if isinstance(sample, int):
+    if isinstance(sample, bool):
+        return Boolean
+    elif isinstance(sample, int):
         return Integer
     elif isinstance(sample, float):
         return Float