[MSDN] Understanding the Table Service Data Model

Understanding the Table Service Data Model

Windows Azure Platform

The Table service offers structured storage in the form of tables. The following sections outline the Table service data model.

Storage Account

A storage account is a globally unique entity within the storage system. The storage account is the parent namespace for the Table service, and is the basis for authentication. You can create any number of tables within a given storage account, as long as each table is uniquely named.

The storage account must always be specified in the request URI. The base URI for accessing the Table service is as follows:

http://myaccount.table.core.windows.net

Tables, Entities, and Properties

Tables store data as collections of entities. Entities are similar to rows. An entity has a primary key and a set of properties. A property is a name, typed-value pair, similar to a column.

The Table service does not enforce any schema for tables, so two entities in the same table may have different sets of properties. Developers may choose to enforce a schema on the client side. A table may contain any number of entities.

Table Names

Table names must conform to these rules:

• Table names may contain only alphanumeric characters.
  
  
• A table name may not begin with a numeric character. 
  
  
• Table names are case-insensitive.
  
  
• Table names must be from 3 through 63 characters long.
  
  

These rules are also described by the regular expression "^[A-Za-z][A-Za-z0-9]*".

Property Names

Property names are case-sensitive and may not exceed 255 characters in size. Property names should follow naming rules for C# identifiers.

Note

Some C# identifiers are not valid according to the XML specification. These identifiers may not be used in property names, as property names are sent via an XML payload in a request against the Table service.

Note

Beginning with version 2009-04-14, the Table service no longer supports including the dash (-) character in property names.

Property Limitations

An entity may have up to 255 properties, including the 3 system properties described in the following section. Therefore, the user may include up to 252 custom properties, in addition to the 3 system properties. The combined size of all data in an entity's properties may not exceed 1 MB.

System Properties

An entity always has the following system properties:

• PartitionKey property
  
  
• RowKey property
  
  
• Timestamp property
  
  

These system properties are automatically included for every entity in a table. The names of these properties are reserved and cannot be changed. The developer is responsible for inserting and updating the values of PartitionKey and RowKey. The server manages the value of Timestamp, which cannot be modified.

Characters Disallowed in Key Fields

The following characters are not allowed in values for the PartitionKey and RowKey properties:

• The forward slash (/) character
  
  
• The backslash (\) character
  
  
• The number sign (#) character 
  
  
• The question mark (?) character
  
  

PartitionKey Property

Tables are partitioned to support load balancing across storage nodes. A table's entities are organized by partition. A partition is a consecutive range of entities possessing the same partition key value. The partition key is a unique identifier for the partition within a given table, specified by the PartitionKey property. The partition key forms the first part of an entity's primary key. The partition key may be a string value up to 1 KB in size.

You must include the PartitionKey property in every insert, update, and delete operation.

RowKey Property

The second part of the primary key is the row key, specified by the RowKey property. The row key is a unique identifier for an entity within a given partition. Together the PartitionKey andRowKey uniquely identify every entity within a table.

The row key is a string value that may be up to 1 KB in size.

You must include the RowKey property in every insert, update, and delete operation.

Timestamp Property

The Timestamp property is a DateTime value that is maintained on the server side to record the time an entity was last modified. The Table service uses the Timestamp property internally to provide optimistic concurrency. You should treat this property as opaque: It should not be read, nor set on insert or update operations (the value will be ignored).

Property Types

The Table service supports a subset of data types defined by the ADO.NET Data Services specification. The following table shows the supported property types for the Table service:

 

ADO.NET Data Services type	Common Language Runtime type	Details
Edm.Binary	byte[]	An array of bytes up to 64 KB in size.
Edm.Boolean	bool	A Boolean value.
Edm.DateTime	DateTime	A 64-bit value expressed as Coordinated Universal Time (UTC). The supported DateTime range begins from 12:00 midnight, January 1, 1601 A.D. (C.E.), UTC. The range ends at December 31, 9999.
Edm.Double	double	A 64-bit floating point value.
Edm.Guid	Guid	A 128-bit globally unique identifier.
Edm.Int32	Int32 or int	A 32-bit integer.
Edm.Int64	Int64 or long	A 64-bit integer.
Edm.String	String	A UTF-16-encoded value. String values may be up to 64 KB in size.

By default a property is created as type String, unless you specify a different type. To explicitly type a property, specify its data type by using the appropriate ADO.NET Data Services type in the Atom feed for an Insert Entity or Update Entity operation. For more information, see Inserting and Updating Entities.

For examples that show how to filter on the various property types in a query request URI, see Querying Tables and Entities.

See Also

Concepts

Table Service Concepts 

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 FAQ

Regular expression for the Table name

It might be better :

"^[A-Za-z][A-Za-z0-9]{2,62}$"

That's the exact match wich in python goes :

import re
name = "myTableName3"
if not re.match('^[A-Za-z][A-Za-z0-9]{2,62}$', name):
    print "Invalid !"