def __find_by_template_scan__(self,
t,
fields=None,
limit=None,
offset=None):
"""
Returns a new, derived table containing rows that match the template and the requested fields if any.
Returns all row if template is None and all columns if fields is None.
:param t: The template representing a select predicate.
:param fields: The list of fields (project fields)
:param limit: Max to return. Not implemented
:param offset: Offset into the result. Not implemented.
:return: New table containing the result of the select and project.
"""
if limit is not None or offset is not None:
raise DataTableExceptions.DataTableException(
-101, "Limit/offset not supported for CSVTable")
# If there are rows and the template is not None
if self.__rows__ is not None:
result = []
# Add the rows that match the template to the newly created table.
for r in self.__rows__:
if self.matches_template(r, t):
result.append(r)
result = self.project(result, fields)
else:
result = None
return result
def project(self, rows, fields):
"""
Perform the project. Returns a new table with only the requested columns.
:param fields: A list of column names.
:return: A new table derived from this table by PROJECT on the specified column names.
"""
try:
if fields is None: # If there is not project clause, return the base table
return rows # Should really return a new, identical table but am lazy.
else:
result = []
for r in rows: # For every row in the table.
tmp = {} # Not sure why I am using range.
for j in range(
0, len(fields)
): # Make a new row with just the requested columns/fields.
v = r[fields[j]]
tmp[fields[j]] = v
else:
result.append(tmp) # Insert into new table when done.
return result
except KeyError as ke:
# happens if the requested field not in rows.
raise DataTableExceptions.DataTableException(
-2, "Invalid field in project")
def __load__(self):
try:
fn = self.__get_file_name__()
with open(fn, "r") as csvfile:
# CSV files can be pretty complex. You can tell from all of the options on the various readers.
# The two params here indicate that "," separates columns and anything in between " ... " should parse
# as a single string, even if it has things like "," in it.
reader = csv.DictReader(csvfile, delimiter=",", quotechar='"')
# Get the names of the columns defined for this table from the metadata.
column_names = self.__get_column_names__()
# Loop through each line (well dictionary) in the input file.
for r in reader:
# Only add the defined columns into the in-memory table. The CSV file may contain columns
# that are not relevant to the definition.
projected_r = self.project([r], column_names)[0]
self.__add_row__(projected_r)
except IOError as e:
raise DataTableExceptions.DataTableException(
code=DataTableExceptions.DataTableException.invalid_file,
message="Could not read file = " + fn)
def update(self, t, change_values):
raise DataTableExceptions.DataTableException(
code=DataTableExceptions.DataTableException.not_implemented,
message="Updated not implemented")
def delete(self, t):
raise DataTableExceptions.DataTableException(
code=DataTableExceptions.DataTableException.not_implemented,
message="Delete not implemented")
def insert(self, r):
raise DataTableExceptions.DataTableException(
code=DataTableExceptions.DataTableException.not_implemented,
message="Insert not implemented")