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Example Problem - Making Sure The Admit Date is Valid |
The previous example illustrates how much easier it is to use Chameleon's built-in Python database functionality to perform validation than it is to use your database's trigger/constraint functionality. Since it is so powerful, another example is in order.
Suppose, whenever we receive an A01 message (Patient Visit), we want to ensure that the information we receive as far as their Admit Date is greater than or equal to the value already in our database for this patient (it should be in most cases). To enforce this constraint, we might write the following Python validation rule into the PV1 segment's 44th field.
# get the field's current value, remember the value
# is always a String in the segment level scripts
AdmitDate = validation_field.value
# since we're going to need to compare the value
# of this field against a date from the database,
# we need to convert the date/time string to a double
# Remember: in Chameleon, date/times are represented as
# floating point numbers
AdmitDateAsDouble = environment.date_time_to_double(AdmitDate, 'Time Stamp')
# Now let's get the value from our database for comparison.
# We'll select the patient's record from our Patient table
# using the MRN (unique identifier) python variable which
# we've already set in our PID segment script.
db = environment.get_default_database()
escapedPatientID = db.escape_string(MRN)
SQL = "select Recent_Case_Start_Date from Patient where MRN = " + escapedPatientID
ResultSet = db.execute_select(SQL)
# Ensure that the patient is in the database, it should be
# since this is an A01 message!
if (ResultSet.count_of_row() > 0):
# Get the date that's already in the database, assume we
# stored the date as "Recent_Case_Start_Date" - ie. that's the
# Chameleon/DB table's column name
AdmitDateInDB = ResultSet.value(0, "Recent_Case_Start_Date")
# If the incoming date is less than the one already in the
# database, reject the message
if (AdmitDateInDB > AdmitDateAsDouble):
Error = chmexception.errorobject
Error.description = "The Admit Date received (" + AdmitDate + ") is less than the one already in the database."
raise chmexception
else:
# Exception indicating the patient isn't in the DB
Error = chmexception.errorobject
Error.description = "Received A01 Message for a Patient (MRN=" + MRN + ") who is not in the Database."
raise chmexception |