I’m using Python to add data to a DynamoDB table named Courses and provide a command-interface for a user to search for a course description by entering the subject and catalog number.
The desired result:
Welcome to the Course Title Navigator Enter Subject: SDEB Enter Catalog Number: 452 Inaccurate search or No records found. Please try again! Enter Subject: SDEV Enter Catalog Number: 450 SDEV 450 is Advanced Programming Would you like to search for another title? Y or N N Thank you for using the Course Title Navigator
I am having issues with my program not returning table attributes after table.scan(). It seems to read the response as 0 and print the error message. I think there’s an issue with my table.scan, but I’m not sure what. I initially was using query, but I was having a ton of issues with it, and I read that scan is more suited for my application.
def check_class_info(Subject, CatalogNbr, Title, dynamodb=None): # checks if class info exists
if not dynamodb:
dynamodb = boto3.resource('dynamodb')
while True:
Subject = ""
CatalogNbr = ""
while Subject == "":
Subject = input ("Enter Subject: ")
CatalogNbr = ""
while CatalogNbr == "":
CatalogNbr = input("Enter Catalog Number: ")
CatalogNbr = int(CatalogNbr)
response = table.scan(FilterExpression=Attr("Subject").eq(Subject) & Attr("CatalogNbr").eq(CatalogNbr))
# print(response)
if response["Count"] == 0:
print ("Inaccurate search or No records found. Please try again!")
return end_main()
else:
print(response["Items"][0]["title"])
return end_main()
Here are the details of my table:
aws dynamodb describe-table --table-name Courses
{
"Table": {
"TableArn": "arn:aws:dynamodb:us-east-1:399520938535:table/Courses",
"AttributeDefinitions": [
{
"AttributeName": "CourseID",
"AttributeType": "S"
},
{
"AttributeName": "Subject",
"AttributeType": "S"
}
],
"ProvisionedThroughput": {
"NumberOfDecreasesToday": 0,
"WriteCapacityUnits": 50,
"ReadCapacityUnits": 50
},
"TableSizeBytes": 753,
"TableName": "Courses",
"TableStatus": "ACTIVE",
"TableId": "d62be64f-949d-454c-b716-93ff18968d58",
"KeySchema": [
{
"KeyType": "HASH",
"AttributeName": "CourseID"
},
{
I’m still learning DynamoDB, so I’m struggling to solve the error. I really appreciate any help you can provide.
Answer
Scan operation can be run in two ways
response = table.scan(FilterExpression=Attr("Subject").eq(Subject) & Attr("CatalogNbr").eq(CatalogNbr))
OR
response = table.scan(
FilterExpression= 'Subject=:subject AND CatalogNbr=:catalogNbr',
ExpressionAttributeValues= {
':subject': Subject ,
':catalogNbr': CatalogNbr,
} )
In both types of syntax we must pass the right type. From the comments, in this case CatalogNbr which is a string in database must be passed as string. Hence removing CatalogNbr = int(CatalogNbr) line worked.