Step 25. Accessing Australian Markets.

To access the Australian exchange you can add another web reference (as described in the note at the bottom of Step 5). This creates the BFAU namespace which contains an identical set of classes to BFUK. This is fine if you want to access the Australian exchange only. You simply create a BFAU web reference and use this (instead of BFUK) throughout your code.

But an app may want access to both UK and AU exchanges. Because BFAU and BFUK are namespaces, not objects, they cannot be simply assigned to variables. This leads to much code duplication. To illustrate this, consider a sub which calls getAllMarkets on either exchange using the separate web references:

Code:

Sub GetAllMarkets(ByVal Ex As Boolean) 'Ex = True for AU, False for UK

If Ex Then 'AU exchange

Dim ReqAU As New BFAU.GetAllMarketsReq

Dim RespAU As BFAU.GetAllMarketsResp

With ReqAU

.header = oHeaderAU()

'Set request parameters here

End With

RespAU = BetfairAU.getAllMarkets(ReqAU) 'Call AU exchange

With RespAU

CheckHeader(.header)

If .errorCode = BFAU.GetAllMarketsErrorEnum.OK Then

'Process response from AU exchange here

Else

Print("ErrorCode = " & .errorCode.ToString)

End If

End With

Else 'UK exchange

Dim ReqUK As New BFUK.GetAllMarketsReq

Dim RespUK As BFUK.GetAllMarketsResp

With ReqUK

.header = oHeaderUK()

'Set request parameters here

End With

RespUK = BetfairUK.getAllMarkets(ReqUK) 'Call UK exchange

With RespUK

CheckHeader(.header)

If .errorCode = BFUK.GetAllMarketsErrorEnum.OK Then

'Process response from UK exchange here

Else

Print("ErrorCode = " & .errorCode.ToString)

End If

End With

End If

End Sub

Here you can see that much of the code is duplicated. You also need the additional BetfairAU service object, the oHeaderAU function and another CheckHeader sub. Problems can also arise when you try to process the response from the two servers. Even though the class BFAU.GetAllMarketsResp is identical to BFUK.GetAllMarketsResp the compiler assumes they are different. This can give rise to all sorts of problems and your code can become very messy. Perhaps some OOP guru can show us a better way of handling the two namespaces.

However, there is another way we can do this. I doubt that this is “best practice” but it works.

What we can do is write the code as if we are accessing the UK exchange only. Only one web reference (BFUK) is required. If we examine the service object BetfairUK we see that it has a .Url property. This property holds the web address (URL) of the server that it will access. By default this is set to the UK exchange server. If we change this, we can “trick” this service object into accessing the AU exchange server.

Code:

Sub GetAllMarkets(ByVal Ex As Boolean) 'Ex = True for AU, False for UK

SelectExchange(Ex) 'Select the desired exchange URL

Dim ReqUK As New BFUK.GetAllMarketsReq

Dim RespUK As BFUK.GetAllMarketsResp

With ReqUK

.header = oHeaderUK()

'Set request parameters here

End With

RespUK = BetfairUK.getAllMarkets(ReqUK) 'Call the exchange (AU or UK)

With RespUK

CheckHeader(.header)

If .errorCode = BFUK.GetAllMarketsErrorEnum.OK Then

'Process response here

Else

Print("ErrorCode = " & .errorCode.ToString)

End If

End With

End Sub

Sub SelectExchange(ByVal Ex As Boolean) 'Ex = True for AU, False for UK

If Ex Then 'AU exchange

BetfairUK.Url = "https://api-au.betfair.com/exchange/v5/BFExchangeService" 'URL of AU exchange

Else 'UK exchange

BetfairUK.Url = "https://api.betfair.com/exchange/v5/BFExchangeService" 'URL of UK exchange

End If

End Sub

Sub SelectExchange selects either the AU or UK exchange by changing the value of the Betfair.Url property. Depending on the value of the parameter Ex the subsequent call to getAllMarkets returns data from the desired exchange.

This "trick" should work for all API exchange calls (although I have not fully tested this).

Date: 2014-12-21; view: 906