How to check if DynamoDB table exists?

问题:

I'm a new user in boto3 and i'm using DynamoDB.

I went through over the DynamoDB api and I couldn't find any method which tell me if a table is already exists.

What is the best approach dealing this issue?

Should I try to create a new table and wrap it using try catch ?

回答1:

From reading the documentation, I can see that there are three methods by which you can check if a table exists.

1. The CreateTable API throws an error ResourceInUseException if the table already exists. Wrap the create_table method with try except to catch this
2. You can use the ListTables API to get the list of table names associated with the current account and endpoint. Check if the table name is present in the list of table names you get in the response.
3. The DescribeTable API will throw an error ResourceNotFoundException if the table name you request doesn't exist.

To me, the first option sounds better if you just want to create a table.

Edit: I see that some people are finding it difficult to catch the exceptions. I will put some code below for you to know how to handle exceptions in boto3.

Example 1

import boto3

dynamodb_client = boto3.client('dynamodb')

try:
    response = dynamodb_client.create_table(
        AttributeDefinitions=[
            {
                'AttributeName': 'Artist',
                'AttributeType': 'S',
            },
            {
                'AttributeName': 'SongTitle',
                'AttributeType': 'S',
            },
        ],
        KeySchema=[
            {
                'AttributeName': 'Artist',
                'KeyType': 'HASH',
            },
            {
                'AttributeName': 'SongTitle',
                'KeyType': 'RANGE',
            },
        ],
        ProvisionedThroughput={
            'ReadCapacityUnits': 5,
            'WriteCapacityUnits': 5,
        },
        TableName='test',
    )
except dynamodb_client.exceptions.ResourceInUseException:
    # do something here as you require
    pass

Example 2

import boto3

dynamodb_client = boto3.client('dynamodb')


table_name = 'test'
existing_tables = dynamodb_client.list_tables()['TableNames']

if table_name not in existing_tables:
    response = dynamodb_client.create_table(
        AttributeDefinitions=[
            {
                'AttributeName': 'Artist',
                'AttributeType': 'S',
            },
            {
                'AttributeName': 'SongTitle',
                'AttributeType': 'S',
            },
        ],
        KeySchema=[
            {
                'AttributeName': 'Artist',
                'KeyType': 'HASH',
            },
            {
                'AttributeName': 'SongTitle',
                'KeyType': 'RANGE',
            },
        ],
        ProvisionedThroughput={
            'ReadCapacityUnits': 5,
            'WriteCapacityUnits': 5,
        },
        TableName=table_name,
    )

Example 3

import boto3

dynamodb_client = boto3.client('dynamodb')

try:
    response = dynamodb_client.describe_table(TableName='test')
except dynamodb_client.exceptions.ResourceNotFoundException:
    # do something here as you require
    pass

回答2:

import boto3

from botocore.exceptions import ClientError

TABLE_NAME = "myTableName"
dynamodb = boto3.resource('dynamodb', endpoint_url="https://dynamodb.us-east-1.amazonaws.com")

table = dynamodb.Table(TABLE_NAME)

try:
    response = client.describe_table(TableName=TABLE_NAME)

except ClientError as ce:
if ce.response['Error']['Code'] == 'ResourceNotFoundException':
    print "Table " + TABLE_NAME + " does not exist. Create the table first and try again."
else:
    print "Unknown exception occurred while querying for the " + TABLE_NAME + " table. Printing full error:"
    pprint.pprint(ce.response)

回答3:

You can use describe table API to determine whether the table exists.

Sample code:

from __future__ import print_function # Python 2/3 compatibility
import os
os.environ["TZ"] = "UTC"
import boto3

client = boto3.client('dynamodb', region_name='us-west-2', endpoint_url="http://localhost:8000")



response = client.describe_table(
    TableName='Movies'
)    

print(response)

If table exists:-

• You will get the response

If table doesn't exists:-

• You will get ResourceNotFoundException

  botocore.errorfactory.ResourceNotFoundException: An error occurred (ResourceNotF oundException) when calling the DescribeTable operation: Cannot do operations on a non-existent table

Another way:-

Waits until this Table is exists. This method calls DynamoDB.Waiter.table_exists.wait() which polls. DynamoDB.Client.describe_table() every 20 seconds until a successful state is reached. An error is returned after 25 failed checks.

table.wait_until_exists()

回答4:

You can use .table_status attr of any boto3 Table instance object. It returns it's status if exists (CREATING, UPDATING, DELETING, ACTIVE) or throws exception botocore.exceptions.ClientError: Requested resource not found: Table: <YOUR_TABLE_NAME> not found. You can wrap those conditions into try / except to have full info on the current table state.

import boto3
from botocore.exceptions import ClientError

dynamodb = boto3.resource('dynamodb', region_name='us-west-2')
table = dynamodb.Table('your_table_name_str')

try:
  is_table_existing = table.table_status in ("CREATING", "UPDATING",
                                             "DELETING", "ACTIVE")
except ClientError:
  is_table_existing = False
  print "Table %s doesn't exist." % table.name

回答5:

Alternate approach if you do not want to use boto3.client but only boto3.resource:

import boto3

database = boto3.resource('dynamodb', endpoint_url="http://localhost:8000")    

table_name  = 'MyTable'
table_names = [table.name for table in database.tables.all()]

if table_name in table_names:
    print('table', table_name, 'exists')