class ProjectPlan(Plan):
"""
The Plan class corresponding to the project
relational algebra operator.
"""
def __init__(self, p: Plan, fieldlist: list):
self._schema = Schema()
self._p = p
for fldname in fieldlist:
self._schema.add(fldname, p.schema())
def open(self):
"""
Creates a project scan for this query.
"""
s = self._p.open()
return ProjectScan(s, self._schema.fields())
def blocks_accessed(self):
"""
Estimates the number of block accesses in the projection,
which is the same as in the underlying query.
"""
return self._p.blocks_accessed()
def records_output(self):
"""
Estimates the number of output records in the projection,
which is the same as in the underlying query.
"""
return self._p.records_output()
def distinct_values(self, fldname):
"""
Estimates the number of distinct field values
in the projection,
which is the same as in the underlying query.
"""
return self._p.distinct_values(fldname)
def schema(self):
"""
Returns the schema of the projection,
which is taken from the field list.
"""
return self._schema
class ProjectPlan(Plan):
"""
The Plan class corresponding to the project
relational algebra operator.
"""
def __init__(self, p: Plan, fieldlist: list):
self._schema = Schema()
self._p = p
for fldname in fieldlist:
self._schema.add(fldname, p.schema())
def open(self):
"""
Creates a project scan for this query.
"""
s = self._p.open()
return ProjectScan(s, self._schema.fields())
def blocks_accessed(self):
"""
Estimates the number of block accesses in the projection,
which is the same as in the underlying query.
"""
return self._p.blocks_accessed()
def records_output(self):
"""
Estimates the number of output records in the projection,
which is the same as in the underlying query.
"""
return self._p.records_output()
def distinct_values(self, fldname):
"""
Estimates the number of distinct field values
in the projection,
which is the same as in the underlying query.
"""
return self._p.distinct_values(fldname)
def schema(self):
"""
Returns the schema of the projection,
which is taken from the field list.
"""
return self._schema
def __init__(self, idxname, leafsch, tx):
"""
Opens a B-tree index for the specified index.
The method determines the appropriate files
for the leaf and directory records,
creating them if they did not exist.
:param idxname: the name of the index
:param leafsch: the schema of the leaf index records
:param tx: the calling transaction
"""
assert isinstance(leafsch, Schema)
assert isinstance(tx, Transaction)
self._tx = tx
self._leaf = None
# deal with the leaves
leaftbl = idxname + "leaf"
self._leaf_ti = TableInfo(leaftbl, leafsch)
if tx.size(self._leaf_ti.file_name() == 0):
tx.append(self._leaf_ti.file_name(), BTPageFormatter(self._leaf_ti, -1))
# deal with the directory
dirsch = Schema()
dirsch.add("block", leafsch)
dirsch.add("dataval", leafsch)
dirtbl = idxname + "dir"
self._dir_ti = TableInfo(dirtbl, dirsch)
self._rootblk = Block(self._dir_ti.file_name(), 0)
if tx.size(self._dir_ti.file_name() == 0):
# create new root block
tx.append(self._dir_ti.file_name(), BTPageFormatter(self._dir_ti, 0))
page = BTreePage(self._rootblk, self._dir_ti, tx)
if page.get_num_recs() == 0:
# insert initial directory entry
fldtype = dirsch.type("dataval")
minval = IntConstant(-sys.maxsize) if fldtype == INTEGER else StringConstant("")
page.insert_dir(0, minval, 0)
page.close()