Why the same query is being executed two times with the two methods? - postgresql

Question

def execCypher(conn:ext.connection, graphName:str, cypherStmt:str, cols:list=None, params:tuple=None) -> ext.cursor :
if conn == None or conn.closed:
raise _EXCEPTION_NoConnection
cursor = conn.cursor()
#clean up the string for modification
cypherStmt = cypherStmt.replace("\n", "")
cypherStmt = cypherStmt.replace("\t", "")
cypher = str(cursor.mogrify(cypherStmt, params))
cypher = cypher[2:len(cypher)-1]
preparedStmt = "SELECT * FROM age_prepare_cypher({graphName},{cypherStmt})"
cursor = conn.cursor()
try:
cursor.execute(sql.SQL(preparedStmt).format(graphName=sql.Literal(graphName),cypherStmt=sql.Literal(cypher)))
except SyntaxError as cause:
conn.rollback()
raise cause
except Exception as cause:
conn.rollback()
raise SqlExecutionError("Execution ERR[" + str(cause) +"](" + preparedStmt +")", cause)
stmt = buildCypher(graphName, cypher, cols)
cursor = conn.cursor()
try:
cursor.execute(stmt)
return cursor
except SyntaxError as cause:
conn.rollback()
raise cause
except Exception as cause:
conn.rollback()
raise SqlExecutionError("Execution ERR[" + str(cause) +"](" + stmt +")", cause)
I just want to understand that if the two execution calls (with preparedStat & buildCypher functions) do the same thing, why are both of them being executed in the same function with same parameters?

Answer 1

The two execution calls are not doing the same thing. SELECT * FROM age_prepare_cypher({graphName},{cypherStmt}) is just storing the graphName and cypherStmt into the session.
The buildCypher function does this, it doesn't even touch your cypherStmt:
def buildCypher(graphName:str, cypherStmt:str, columns:list) ->str:
if graphName == None:
raise _EXCEPTION_GraphNotSet
columnExp=[]
if columns != None and len(columns) > 0:
for col in columns:
if col.strip() == '':
continue
elif WHITESPACE.search(col) != None:
columnExp.append(col)
else:
columnExp.append(col + " agtype")
else:
columnExp.append('v agtype')
stmtArr = []
stmtArr.append("SELECT * from cypher(NULL,NULL) as (")
stmtArr.append(','.join(columnExp))
stmtArr.append(");")
return "".join(stmtArr)
Later on it must be getting the graphName and cypherStmt back out of the session to use. So it needs both of them to work.
See more at https://stackoverflow.com/a/75461986/6796081