Feature: Upsert Table Entity: Support Changing Existing Entities

Using Binding alone, it is not possible to modify a Table Entity.

#### Investigative information

Please provide the following:

- Timestamp: 2017-07-07T13:37:47.269
- Function App name: told-stack-demo
- Function name(s) (as appropriate): http-to-table
- Invocation ID: 8fe9fdae-6907-4cb2-9982-de43a7a4e5f2
- Region: East US 2

```
2017-07-07T13:37:47.269 Function started (Id=8fe9fdae-6907-4cb2-9982-de43a7a4e5f2)
2017-07-07T13:37:49.815 Function completed (Success, Id=8fe9fdae-6907-4cb2-9982-de43a7a4e5f2, Duration=2547ms)
2017-07-07T13:37:50.002 Exception while executing function: Functions.http-to-table. Microsoft.Azure.WebJobs.Host: Error while handling parameter _binder after function returned:. Microsoft.WindowsAzure.Storage: The specified entity already exists.
RequestId:756cc6df-0002-0065-4726-f70b5c000000
Time:2017-07-07T13:37:49.6169943Z.
```

#### Repro steps

1. Bind to a Table with 'out' direction
2. Use an existing PartitionKey and RowKey

#### Expected behavior

Provide a description of the expected behavior.

- InsertOrMerge Behavior:
- If no row exists, insert it
- If a row exists, replace column values with provided values

#### Actual behavior

Provide a description of the actual behavior observed.

```
2017-07-07T13:37:50.002 Exception while executing function: Functions.http-to-table. Microsoft.Azure.WebJobs.Host: Error while handling parameter _binder after function returned:. Microsoft.WindowsAzure.Storage: The specified entity already exists.
```

#### Known workarounds

Provide a description of any known workarounds.

- Use the Azure Storage SDK

Problems with the Workaround:

- with Node this requires bundling and adds 2MB to the script size
- bundling is required because of poor performance with node_modules

#### Related information

Provide any related information

- Typescript
- Node.js

Source

function.json:

```json

{
"bindings": [
{
"name": "req",
"type": "httpTrigger",
"direction": "in",
"authLevel": "anonymous",
"route": "api/http-to-table/{table}/{partition}/{row}"
},
{
"name": "res",
"type": "http",
"direction": "out"
},
{
"name": "inOutputTable",
"type": "table",
"direction": "in",
"tableName": "{table}",
"partitionKey": "{partition}",
"rowKey": "{row}",
"connection": "AZURE_STORAGE_CONNECTION_STRING"
},
{
"name": "outOutputTable",
"type": "table",
"direction": "out",
"tableName": "{table}",
"partitionKey": "{partition}",
"rowKey": "{row}",
"connection": "AZURE_STORAGE_CONNECTION_STRING"
}
],
"disabled": false
}

```

This is an attempt to mimic what was reported to work in C# at:

https://stackoverflow.com/a/44900064/567524

```typescript

if (context.bindings.inOutputTable) {
context.bindings.outOutputTable = context.bindings.inOutputTable;
for (let k in data) {
context.bindings.outOutputTable[k] = data[k];
}
} else {
context.bindings.outOutputTable = data;
}

```

Use the supplied function.json reproduction with Azure Table input and output bindings as the starting point. Inspect how table output bindings handle an existing entity, then verify the requested InsertOrMerge behavior: update matching PartitionKey and RowKey values while inserting when no row exists.

Written by the indexing model from the issue text.