In azure table storage is it possible to add a unique constraint on a column of a given table?
Azure Table Storage entities don't have columns. Each entity may have properties and these properties don't need to be the same for each entity.
The only unique constraint is the combination of partition key + row key.
There's an excellent article on Azure table storage here:
http://msdn.microsoft.com/en-us/library/windowsazure/dd179338.aspx
Since it only has a Row Key and a Partition Key, and the Row Key is essentially the primary key, it doesn't look like there's any other constraint you can put on it unless you build that sort of thing into your client/server which uses or exposes it.
From the article:
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.
HTH :)
Related
can we sync two tables of two different databases in azure without indexes. As, we all know ,if two databases has to be in sync hub database and member data base should have same schema. But is there chance of avoiding indexes.
please help me with this
Each table needs to have a primary key and you cannot avoid that. Please read the following excerpt from Microsoft documentation:
Each table must have a primary key. Don't change the value of the
primary key in any row. If you have to change a primary key value,
delete the row and recreate it with the new primary key value.
Source here.
I think this is not possible, but however I ask the question, maybe I have missed something.
Can we add/remove columns from an azure table?
For example by default we get those columns: PartitionKey, RowKey, Timestamp, ETag. Can I add for example another 3: FirstName, LastName, Email columns?
After that I will insert some values and I want to remove column Email and add instead column Address. Can we do this?
As Igor rightly said, Azure Tables do not have the concept of rows and columns. A table can contain zero or more entities and each entity can have a maximum of 255 attributes (an attribute is a name/value/type). Off of these 255 attributes, 3 of them are system attributes (PartitionKey, RowKey and Timestamp) which you can't update through your code. When creating an entity you define PartitionKey and RowKey and after that they become readonly properties. So when it comes to updating an entity, you can only update 252 attributes.
To manage data in an Azure Table, there's a REST API and you provide attributes of an entity in the request body. Azure Storage provides two ways by which you can update an entity - Update and Merge.
When you tell Azure Table Service to Update an entity, it simply drops all the existing attributes for that entity, and inserts the attributes defined in the request payload.
When you tell Azure Table Service to Merge an entity, it looks at the existing entity attributes and compares them with the attributes defined in the request payload. If it finds matching attributes, it simply updates those attributes. If the attributes are not present in existing entity but are defined in request payload, those attributes get added to the entity. If the attribute are present in existing entity but are not defined in request payload, they are not changed.
Now coming to your problem.
So let's say you already have an entity where you just defined PartitionKey and RowKey. Now you want to add FirstName, LastName, Email attributes. Because these attributes are not there in the entity, you can either use Merge or Replace to update the entity and these attributes will be added to the entity.
Now you want to drop Email attribute from an entity and instead add Address attribute to that entity. What you will do is perform an Update operation on that entity where your request body will have FirstName, LastName and Address attributes only (no Email attribute). When you update the entity with this request payload, Email attribute will be removed from the entity.
Azure Tables do not have "columns" as SQL tables do. Azure Tables have entities. Each entity has up to 255 properties. Most tools that let you look at an Azure table, choose to visualize the data in it tabular with columns. However, in reality, each entity (row) is a collection of properties.
Therefore, you can save objects/entities into an Azure Table with different properties, everytime you do a save. It makes things somewhat confusing, but you can do it.
HTH
I think programmatic answers given above is the best solution in terms of achieving the functionality.
But in case, you are working in the development mode and you have inserted an unnecessary attribute which you want to remove. you can do the same by using azure storage explorer.
You can export the table of choice, delete the property in the CSV file and import it back in new table. drop the existing table and rename the new table to the existing one. This is kind of a work around.
I am creating account data in Cassandra. Accounts are most commonly queried based on an account id. However, often the account is queried by a login name. I have created a user table with primary keys (account_id and login_name). Because of this, I have to "ALLOW FILTERING" on the table to query by the login_name.
Is there a better way to create the table that does not have the impact of a filterable table?
A possible approach is to define a new table that has the exact same elements in the primary key but in the reverse order: (login_name, account_id). You can still keep the table you present as the reference table, which stores all the relevant account data, but this new table would allow you more optimized queries based on login_name. I am not sure how much you would win compared with the query "allowing filtering"... But this kind of "data duplication" for query optimization is a normal procedure in NoSQL DBs.
HTH.
Each user of my system can have contacts. Each contact has details like Name, Address, Email, Phone, etc.
Do you think is a good idea to store this contacts in Azure Tables? I am worried about the following:
How do I search for a specific field (like Email or Phone)?
How do I get only the contacts belonging to a specific user?
How do I sort the contacts by a field?
I think that contacts could be a good candidate for storing in Table Storage - but only if you can partition on the owning person and never really need to search or aggregate across multiple owning users.
One possible design for this is:
store the contacts once with the owning user as partition key and some unique field for row key, but with the fields as columns within each row.
How do I search for a specific field (like Email or Phone)?
You can then ask table storage to search within a partition - it will then do a scan within that partition - which shouldn't be particularly large or slow for any single partition.
How do I get only the contacts belonging to a specific user?
This is just a simple query by partition key only
How do I sort the contacts by a field?
All results from table storage are sorted by (partitionkey, rowkey) so to sort the contacts for a user, you'll need to query for all of them, and then sort them within your web or worker role.
Other designs are, of course, possible -
e.g. you could store each contact in multiple rows in multiple tables - this would then allow you to have pre-formed sort orders within the table storage.
e.g. you could use separate tables instead of separate partitionkeys for each user - this has the advantage that when you delete a user, you can delete the entire table belonging to that user.
Note... while it's possible to use table storage for this... actually I almost always seem to end up back in SQL Azure at the moment - it's just so much more powerful and predictable (IMO). When the team deliver secondary indexing, then I might be tempted to use it for more of my data.
I have two sharepoint List.
List1 - This contains all users and has primary key as UserId
List2 - This contains all courses and has primary key as CourseId
Now I want to define third list that would have its primary key as composite key.
List3 - This contains users to courses mapping. So the primary key is (UserId, CourseId) combination.
When I define List3, I add columns from the List Settings page. When I create a new column, I can choose Lookup and choose the foreign key from another list. But I am unable to define a composite key. (where the keys come from different list).
Is there a way to define composite key for a list in sharepoint 2010?
Thanks
Sharepoint is not a database and lists are not tables. There are no primary, foreign keys or relations (in the DB sense) in Sharepoint. While the DB metaphor is used to explain Sharepoint it is just an metaphor, not the way Sharepoint works. The closest thing to Sharepoint you can find in the database world are document databases.
Perhaps you are confusing lookup fields with primary keys. A lookup field is a field whose values come from another list. They do not define a relation between the lists. That said, Sharepoint 2010 allows you to enforce deletion constraints so that you can't delete a list item that is used as a lookup value in another list. This is set at the lookup field level and only if the lookup field allows a single choice.
To set the restriction programmatically, use the SPFieldLookup.RelationshipDeleteBehavior property. To set the restriction from the UI, locate the lookup field in the target list's settings, open its settings and enable "Enforce Relationship Behavior" in the Relations section.