Azure Cosmos DB 列数限制

Question

The Azure Table Service documentation states that entities (rows) must have at most 255 properties, which I understand to mean these tables can have at most 255 columns, which seems highly restrictive.

Two questions: first, do the same limits apply to Cosmos DB Table Storage? I can't seem to find any documentation that says one way or another, though the language of "entities" is still used. And second--if the same limit applies in Cosmos DB--is there any useful way around this limit for storage and querying, along the lines of JSON in SQL Server ?

EDIT: here is some example code that attempts to write entities with 260 properties to Cosmos DB Table Storage and the error that is thrown. Account names and keys and such are redacted

# Libraries
from azure.cosmosdb.table.tableservice import TableService
from azure.cosmosdb.table.models import Entity
import csv
import os


# Connect
## Table Storage
"""
access_key = 'access_key'
table_service = TableService(account_name='account_name', account_key= access_key)
"""
## Cosmos DB Table Storage
connection_string = "connection_string"
table_service = TableService(connection_string=connection_string)

# Create Table
if not table_service.exists('testTable'):
    table_service.create_table('testTable')

length = 260
letters = [chr(i) for i in range(ord('a'), ord('z') + 1)]
keys = [a + b + c for a in letters for b in letters for c in letters][:length] 
values = ['0' * (8 - len(str(i))) + str(i) for i in range(length)]
entity = dict(zip(keys, values))
entity['PartitionKey'] = 'TestKey'
entity['RowKey'] = '1'
table_service.insert_entity('testTable', entity)

This raises "ValueError: The entity contains more properties than allowed."

Answer 1

first, do the same limits apply to Cosmos DB Table Storage?

Based on the Azure Table storage limits , as you said ,max number of properties in a table entity is 255 . However,I just found below statement in Azure Cosmos DB limits .

Azure Cosmos DB is a global scale database in which throughput and storage can be scaled to handle whatever your application requires. If you have any questions about the scale Azure Cosmos DB provides, please send email to askcosmosdb@microsoft.com.

According to my test(I tired to add 260 properties into an entity), Azure Cosmos DB Table API accept that properties exceed 255.

If you want to get official reply, you could send email to above address.

is there any useful way around this limit for storage and querying, along the lines of JSON in SQL Server?

If you want to store and query data of json format, I suggest you using cosmos db SQL API.It is versatile and flexible.You could refer to the doc .

Besides, if your data are stored in sql server database now. You could use Migration Tool to import data into cosmos db. Or you could Azure Data Factory to do more custom transmission.

Hope it helps you.

Answer 2

Since this pops pretty high on Google searches: As of now, it's 255 (-2 if you encrypt)

I just did a quick test using pytest:

from azure.cosmosdb.table import TableService
field_number = 250
entity = get_dummy_dict_entry_with_many_col(field_number)
for x in range(field_number, 1000):
    print("Adding entity with {} elements.".format(len(entity)))
    table_service.insert_entity(my_test_table_name, entity)
    field_number += 1
    entity["Field_nb_{}".format(field_number)] = field_number
    entity["RowKey"] += str(field_number)

and got an exception in "def _validate_entity(entity, encrypt=None):"

# Two properties are added during encryption. Validate sufficient space
max_properties = 255
if encrypt:
    max_properties = max_properties - 2  
# Validate there are not more than 255 properties including Timestamp
    if (len(entity) > max_properties) or (len(entity) == max_properties and 'Timestamp' not in entity):
>           raise ValueError(_ERROR_TOO_MANY_PROPERTIES)
E           ValueError: The entity contains more properties than allowed.