[ENH] SQL Server support in SQL widget

Orange/data/sql/__init__.py

@@ -1,2 +0,0 @@
-import Orange.misc
-psycopg2 = Orange.misc.import_late_warning("psycopg2")

Orange/data/sql/backend/__init__.py

@@ -0,0 +1,11 @@
+from .base import Backend
+
+try:
+    from .postgres import Psycopg2Backend
+except ImportError:
+    pass
+
+try:
+    from .mssql import PymssqlBackend
+except ImportError:
+    pass

Orange/data/sql/backend/base.py

@@ -0,0 +1,238 @@
+import logging
+from contextlib import contextmanager
+
+from Orange.util import Registry
+
+log = logging.getLogger(__name__)
+
+
+class BackendError(Exception):
+    pass
+
+
+class Backend(metaclass=Registry):
+    """Base class for SqlTable backends. Implementations should define
+    all of the methods defined below.
+
+    Parameters
+    ----------
+    connection_params: dict
+        connection params
+    """
+
+    display_name = ""
+
+    def __init__(self, connection_params):
+        self.connection_params = connection_params
+
+    @classmethod
+    def available_backends(cls):
+        """Return a list of all available backends"""
+        return cls.registry.values()
+
+    # "meta" methods
+
+    def list_tables_query(self, schema=None):
+        """Return a list of tuples (schema, table_name)
+
+        Parameters
+        ----------
+        schema : Optional[str]
+            If set, only tables from schema should be listed
+
+        Returns
+        -------
+        A list of tuples
+        """
+        raise NotImplementedError
+
+    def list_tables(self, schema=None):
+        """Return a list of tables in database
+
+        Parameters
+        ----------
+        schema : Optional[str]
+            If set, only tables from given schema will be listed
+
+        Returns
+        -------
+        A list of TableDesc objects, describing the tables in the database
+        """
+        query = self.list_tables_query(schema)
+        with self.execute_sql_query(query) as cur:
+            tables = []
+            for schema, name in cur.fetchall():
+                sql = "{}.{}".format(
+                    self.quote_identifier(schema),
+                    self.quote_identifier(name)) if schema else self.quote_identifier(name)
+                tables.append(TableDesc(name, schema, sql))
+            return tables
+
+    def get_fields(self, table_name):
+        """Return a list of field names and metadata in the given table
+
+        Parameters
+        ----------
+        table_name: str
+
+        Returns
+        -------
+        a list of tuples (field_name, *field_metadata)
+        both will be passed to create_variable
+        """
+        query = self.create_sql_query(table_name, ["*"], limit=0)
+        with self.execute_sql_query(query) as cur:
+            return cur.description
+
+    def get_distinct_values(self, field_name, table_name):
+        """Return a list of distinct values of field
+
+        Parameters
+        ----------
+        field_name : name of the field
+        table_name : name of the table or query to search
+
+        Returns
+        -------
+        List[str] of values
+        """
+        fields = [self.quote_identifier(field_name)]
+
+        query = self.create_sql_query(table_name, fields,
+                                      group_by=fields, order_by=fields,
+                                      limit=21)
+        with self.execute_sql_query(query) as cur:
+            values = cur.fetchall()
+        if len(values) > 20:
+            return ()
+        else:
+            return tuple(str(x[0]) for x in values)
+
+    def create_variable(self, field_name, field_metadata,
+                        type_hints, inspect_table=None):
+        """Create variable based on field information
+
+        Parameters
+        ----------
+        field_name : str
+            name do the field
+        field_metadata : tuple
+            data to guess field type from
+        type_hints : Domain
+            domain with variable templates
+        inspect_table : Option[str]
+            name of the table to expect the field values or None
+            if no inspection is to be performed
+
+        Returns
+        -------
+        Variable representing the field
+        """
+        raise NotImplementedError
+
+    def count_approx(self, query):
+        """Return estimated number of rows returned by query.
+
+        Parameters
+        ----------
+        query : str
+
+        Returns
+        -------
+        Approximate number of rows
+        """
+        raise NotImplementedError
+
+    # query related methods
+
+    def create_sql_query(
+            self, table_name, fields, filters=(),
+            group_by=None, order_by=None, offset=None, limit=None,
+            use_time_sample=None):
+        """Construct an sql query using the provided elements.
+
+        Parameters
+        ----------
+        table_name : str
+        fields : List[str]
+        filters : List[str]
+        group_by: List[str]
+        order_by: List[str]
+        offset: int
+        limit: int
+        use_time_sample: int
+
+        Returns
+        -------
+        string containing sql query
+        """
+        raise NotImplementedError
+
+    @contextmanager
+    def execute_sql_query(self, query, params=None):
+        """Context manager for execution of sql queries
+
+        Usage:
+            ```
+            with backend.execute_sql_query("SELECT * FROM foo") as cur:
+                cur.fetch_all()
+            ```
+
+        Parameters
+        ----------
+        query : string
+            query to be executed
+        params: tuple
+            parameters to be passed to the query
+
+        Returns
+        -------
+        yields a cursor that can be used to access the data
+        """
+        raise NotImplementedError
+
+    def quote_identifier(self, name):
+        """Quote identifier name so it can be safely used in queries
+
+        Parameters
+        ----------
+        name: str
+            name of the parameter
+
+        Returns
+        -------
+        quoted parameter that can be used in sql queries
+        """
+        raise NotImplementedError
+
+    def unquote_identifier(self, quoted_name):
+        """Remove quotes from identifier name
+        Used when sql table name is used in where parameter to
+        query special tables
+
+        Parameters
+        ----------
+        quoted_name : str
+
+        Returns
+        -------
+        unquoted name
+        """
+        raise NotImplementedError
+
+
+class TableDesc:
+    def __init__(self, name, schema, sql):
+        self.name = name
+        self.schema = schema
+        self.sql = sql
+
+    def __str__(self):
+        return self.name
+
+class ToSql:
+    def __init__(self, sql):
+        self.sql = sql
+
+    def __call__(self):
+        return self.sql

Orange/data/sql/backend/mssql.py

@@ -0,0 +1,118 @@
+from contextlib import contextmanager
+
+import pymssql
+
+from Orange.data import StringVariable, TimeVariable, ContinuousVariable, DiscreteVariable
+from Orange.data.sql.backend import Backend
+from Orange.data.sql.backend.base import ToSql, BackendError
+
+
+class PymssqlBackend(Backend):
+    display_name = "SQL Server"
+
+    def __init__(self, connection_params):
+        connection_params["server"] = connection_params.pop("host", None)
+
+        for key in list(connection_params):
+            if connection_params[key] is None:
+                del connection_params[key]
+
+        super().__init__(connection_params)
+        try:
+            self.connection = pymssql.connect(**connection_params)
+        except pymssql.Error as ex:
+            raise BackendError(str(ex)) from ex
+
+    def list_tables_query(self, schema=None):
+        return """
+        SELECT [TABLE_SCHEMA], [TABLE_NAME]
+          FROM information_schema.tables
+         WHERE TABLE_TYPE='BASE TABLE'
+      ORDER BY [TABLE_NAME]
+        """
+
+    def quote_identifier(self, name):
+        return "[{}]".format(name)
+
+    def unquote_identifier(self, quoted_name):
+        return quoted_name[1:-1]
+
+    def create_sql_query(self, table_name, fields, filters=(),
+                         group_by=None, order_by=None, offset=None, limit=None,
+                         use_time_sample=None):
+        sql = ["SELECT"]
+        if limit and not offset:
+            sql.extend(["TOP", str(limit)])
+        sql.append(', '.join(fields))
+        sql.extend(["FROM", table_name])
+        if use_time_sample:
+            sql.append("TABLESAMPLE system_time(%i)" % use_time_sample)
+        if filters:
+            sql.extend(["WHERE", " AND ".join(filters)])
+        if group_by:
+            sql.extend(["GROUP BY", ", ".join(group_by)])
+
+        if offset and not order_by:
+            order_by = fields[0].split("AS")[1:]
+
+        if order_by:
+            sql.extend(["ORDER BY", ",".join(order_by)])
+        if offset:
+            sql.extend(["OFFSET", str(offset), "ROWS"])
+            if limit:
+                sql.extend(["FETCH FIRST", str(limit), "ROWS ONLY"])
+
+        return " ".join(sql)
+
+    @contextmanager
+    def execute_sql_query(self, query, params=()):
+        print(query)
+        try:
+            with self.connection.cursor() as cur:
+                cur.execute(query, *params)
+                yield cur
+        finally:
+            self.connection.commit()
+
+    def create_variable(self, field_name, field_metadata, type_hints, inspect_table=None):
+        if field_name in type_hints:
+            var = type_hints[field_name]
+        else:
+            var = self._guess_variable(field_name, field_metadata,
+                                       inspect_table)
+
+        field_name_q = self.quote_identifier(field_name)
+        if var.is_continuous:
+            if isinstance(var, TimeVariable):
+                var.to_sql = ToSql("DATEDIFF(s, '1970-01-01 00:00:00', {})".format(field_name_q))
+            else:
+                var.to_sql = ToSql(field_name_q)
+        else:  # discrete or string
+            var.to_sql = ToSql(field_name_q)
+        return var
+
+    def _guess_variable(self, field_name, field_metadata, inspect_table):
+        from pymssql import STRING, NUMBER, DATETIME, DECIMAL
+
+        type_code, *rest = field_metadata
+
+        if type_code in (NUMBER, DECIMAL):
+            return ContinuousVariable(field_name)
+
+        if type_code == DATETIME:
+            tv = TimeVariable(field_name)
+            tv.have_date = True
+            tv.have_time = True
+            return tv
+
+        if type_code == STRING:
+            if inspect_table:
+                values = [] #self._get_distinct_values(field_name, inspect_table)
+                if values:
+                    return DiscreteVariable(field_name, values)
+
+        return StringVariable(field_name)
+
+    def count_approx(self, query):
+        # TODO: Figure out how to do count estimates on mssql
+        raise NotImplementedError