azure logic app with table storage get last rowKey - sorting

Question

How can I use the "Get Entity for Azure table storage" connector in a Logic App to return the last rowKey.
This would be used in situation where the rowkey is say an integer incremented each time a new entity is added. I recognize the flaw in design of this but this question is about how some sort of where clause or last condition could be used in the Logic app.
Currently the Logic App code view snippet looks like this:
"actions": {
"Get_entity": {
"inputs": {
"host": {
"connection": {
"name": "#parameters('$connections')['azuretables']['connectionId']"
}
},
"method": "get",
"path": "/Tables/#{encodeURIComponent('contactInfo')}/entities(PartitionKey='#{encodeURIComponent('a')}',RowKey='#{encodeURIComponent('b')}')"
},
"runAfter": {},
"type": "ApiConnection"
}
Where I have the hard coded:
RowKey='#{encodeURIComponent('b')}'
This is fine if I always want this rowKey. What I want though is the last rowKey so something sort of like:
RowKey= last(RowKey)
Any idea on how this can be achieved?

Answer 1

This is fine if I always want this rowKey. What I want though is the last rowKey so something sort of like: RowKey= last(RowKey)
AFAIK, there is no build-in functions for you to achieve this purpose. I assumed that you could use the Azure Functions connector to retrieve the new RowKey value. Here are the detailed steps, you could refer to them:
For test, I created a C# Http Trigger function, then add a Azure Table Storage Input, then retrieve all the items under the specific PartitionKey, then order by the RowKey and calculate the new Row Key.
function.json:
{
"bindings": [
{
"authLevel": "function",
"name": "req",
"type": "httpTrigger",
"direction": "in"
},
{
"name": "$return",
"type": "http",
"direction": "out"
},
{
"type": "table",
"name": "inputTable",
"tableName": "SampleTable",
"take": 50,
"connection": "AzureWebJobsDashboard",
"direction": "in"
}
],
"disabled": false
}
run.csx:
#r "Microsoft.WindowsAzure.Storage"
using Microsoft.WindowsAzure.Storage.Table;
using System.Net;
public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, IQueryable<SampleTable> inputTable,TraceWriter log)
{
log.Info("C# HTTP trigger function processed a request.");
// parse query parameter
string pk = req.GetQueryNameValuePairs()
.FirstOrDefault(q => string.Compare(q.Key, "pk", true) == 0)
.Value;
// Get request body
dynamic data = await req.Content.ReadAsAsync<object>();
// Set name to query string or body data
pk = pk ?? data?.pk;
if(pk==null)
return req.CreateResponse(HttpStatusCode.BadRequest, "Please pass a pk on the query string or in the request body");
else
{
var latestItem=inputTable.Where(p => p.PartitionKey == pk).ToList().OrderByDescending(i=>Convert.ToInt32(i.RowKey)).FirstOrDefault();
if(latestItem==null)
return req.CreateResponse(HttpStatusCode.OK,new{newRowKey=1});
else
return req.CreateResponse(HttpStatusCode.OK,new{newRowKey=int.Parse(latestItem.RowKey)+1});
}
}
public class SampleTable : TableEntity
{
public long P1 { get; set; }
public long P2 { get; set; }
}
Test:
For more details about Azure Functions Storage table bindings, you could refer to here.

Answer 2

azure table storage entities are sorted lexicographically. So choose a row key that actually decrements every time you add a new entity, ie. if your row key is an integer that gets incremented when new entity is created than choose your row key as Int.Max - entity.RowKey. The latest entity for that partition key will always be on the top since it is going to have the lowest row key, so all you need to do then to retrieve it is query only with partition key and Take(1). This is called Log Tail pattern, if you want to read more about it.