Question

With azure tables, if I know an entity’s RowKey and PartitionKey (so I can retrieve that entity), how do I edit a particular property value on that entity?

This sounds like a pretty standard operation to do, but the normal way of doing it is something like:

public void UpdateEntity(ITableEntity entity)
{
    TableOperation replaceOperation = TableOperation.Replace(entity);
    table.Execute(replaceOperation);
}

i.e. a whole C# TableEntity object is given as a replacement, rather than an individual property name/value pair.

I want something more like:

public void UpdateEntityProperty<T>(string partitionKey, string rowKey,
                                string propertyName, T newPropertyValue)
{
    TableOperation retrieveOperation = TableOperation.Retrieve(partitionKey, rowKey);
    TableResult retrievedResult = table.Execute(retrieveOperation);
    TableEntity entity = (TableEntity)retrievedResult.Result;

    // This  line, of course, doesn't compile. But you get the idea.
    entity.SetPropertyValue(propertyName, newPropertyValue);

    TableOperation replaceOperation = TableOperation.Replace(entity);
    table.Execute(replaceOperation);
}

My understanding is that behind the scenes, the rows are stored as a set of key-value pairs corresponding to properties on that row, so updating a property’s value should be easy without having to define a whole C# class deriving from TableEntity to do so.

How would I do this?

Answer 1

Instead of “Replace” operation, do a “Merge” operation (http://msdn.microsoft.com/en-us/library/windowsazure/microsoft.windowsazure.storage.table.tableoperation.merge). Merge operation will ensure that only the property being modified is changed leaving all other properties unchanged.

public void UpdateEntityProperty<T>(string partitionKey, string rowKey,
                                    string propertyName, T newPropertyValue)
{
    TableOperation retrieveOperation = TableOperation.Retrieve(partitionKey, rowKey);
    TableResult retrievedResult = table.Execute(retrieveOperation);
    TableEntity entity = (TableEntity)retrievedResult.Result;

    // This  line, of course, doesn't compile. But you get the idea.
    entity.SetPropertyValue(propertyName, newPropertyValue);

    TableOperation mergeOperation = TableOperation.Merge(entity);
    table.Execute(mergeOperation);
}

A more complete example below. Here I first created an employee and then only changed the “MaritalStatus” property of that employee:

CloudStorageAccount storageAccount = CloudStorageAccount.DevelopmentStorageAccount;

CloudTable table = storageAccount.CreateCloudTableClient().GetTableReference("Employee");
DynamicTableEntity entity = new DynamicTableEntity()
{
    PartitionKey = "Employee",
    RowKey = "01",
};
Dictionary<string, EntityProperty> properties = new Dictionary<string, EntityProperty>();
properties.Add("Name", new EntityProperty("John Smith"));
properties.Add("DOB", new EntityProperty(new DateTime(1971, 1, 1)));
properties.Add("MaritalStatus", new EntityProperty("Single"));
entity.Properties = properties;

TableOperation insertOperation = TableOperation.Insert(entity);
table.Execute(insertOperation);

DynamicTableEntity updatedEntity = new DynamicTableEntity()
{
    PartitionKey = "Employee",
    RowKey = "01",
    ETag = "*",
};
Dictionary<string, EntityProperty> newProperties = new Dictionary<string, EntityProperty>();
newProperties.Add("MaritalStatus", new EntityProperty("Married"));
updatedEntity.Properties = newProperties;
TableOperation mergeOperation = TableOperation.Merge(updatedEntity);
table.Execute(mergeOperation);

You can also try InsertOrMerge (http://msdn.microsoft.com/en-us/library/windowsazure/microsoft.windowsazure.storage.table.tableoperation.insertormerge.aspx) operation as well.