Read Blob object from DB and convert to System.Collection.Generic.List type of object.

[mugheessiddiqui]

I have scenario where database field stores a System.Collection.Generic.List of Double object. Now I want to read a BLOB object from database field and convert it to list of Array or any type collection in Test Complete. I have written following routine and getting null value when reading a field from record set. Can any body help how to read blob object?

function TestBlob()
{
  var serverName = "ServerName";
  var dbName = "databaseName";
  
  Conn = new ActiveXObject("ADODB.Connection");  
  Conn.ConnectionString = "Driver={SQL Server};Server=" + serverName + 
                          ";Database=" + dbName + ";Trusted_Connection=True;";
  Conn.Open();
  
  var adoCmd = new ActiveXObject("ADODB.Command");
    adoCmd.ActiveConnection = Conn;    
    adoCmd.CommandType = adCmdText;
    adoCmd.CommandText = "Select * from scan";
    var rs = adoCmd.Execute();
    
//Table Field "slices" is type of varbinary 
// and holds the Blob object of System.Collections.Generic.List of Doubles.
   
  rs.MoveFirst();
  var blob = rs.Fields("slices").Value; // Always returns null.
  
  //How can I get coverted Blob object to List of Array, I have tried to test following statement.
  //I have doubt that it will not work. 
  var objList = Aliases.appName.AppDomain("appUI.exe").dotNET.System_Collections_Generic.List_1.zctor_3(blob);

}

[tristaanogre · Accepted solution]

Rather than "Value", you might want to use the GetChunk method.  What you'll need to do is get the ActualSize of the field and then use GetChunk to retrieve it.  I've not tested this but it might look something like this:

 rs.MoveFirst();
var blobSize = rs.Fields("slices").ActualSize;
  var blob = rs.Fields("slices").GetChunk(blobSize);

[AlexKaras]

Sample code example for Robert's reply:

https://docs.microsoft.com/en-us/sql/ado/reference/ado-api/appendchunk-and-getchunk-methods-example-...

[mugheessiddiqui]

Thanks Now I have gotten Blob object.

Second Issue is to Cast the Blob object in some list/dictionary type object of JavaScript for traversing. As I told you we have stored blob object type of System.Collection.Generic.List of Double.

I have found the following description of System.Collection.Generic.List that takes the "<CLRType> collection" object. I don't know how to define <CLRType> collection object.

Description: System.Collection.Generic.List`1 zctor_3(<CLRType> collection);

So far code looks like and I get type Mismatch error.

rs.MoveFirst();

var blobSize = rs.Fields("slices").ActualSize;
var blob = rs.Fields("slices").GetChunk(blobSize);


var objList = Aliases.appName.AppDomain("appUI.exe").dotNET.System_Collections_Generic.List_1.zctor_3(blob); // Gives "Type Mismatch Error"

[tristaanogre]

if your Blob is an image, it's not a collection.  A collection is an object that has fields and properties and items.  At least, that's my understanding.

I don't know the specific collection object you are trying to use so I can't help you further.

[mugheessiddiqui]

No Blob is not an image, it's an serialized object of System.Collections.Generic.List.

[AlexKaras]

Hi,

I am not absolutely sure, but I think that you should:

-- Register relevant (system.dll?) .Net assembly in dotNet Bridge in TestComplete and

-- Use something like

var objList = dotNET.System_Collections_Generic.List_1.zctor_3(blob);

in your code.

As a result, objList variable should contain deserialized list of doubles that cannot be used 'as is' in your test code and must be converted to array or delimited string or something like that that can be iterated and used in JScript.

[HKosova]

Can you ask the developers what code they are using to serialize the list into the DB? This should give you the best idea of how to do the opposite.

Maybe you need to use BinaryFormatter.Deserialize as shown here:
http://stackoverflow.com/questions/2949666/deserialize-stream-to-listt-or-any-other-type
http://stackoverflow.com/questions/26383711/serialize-deserialize-a-list-of-objects-using-binaryform...
http://stackoverflow.com/questions/18876229/serializing-and-deserializing-a-listlistobject-with-bina...
http://stackoverflow.com/questions/33724860/deserialize-list-of-objects-from-a-file-to-be-displayed

Maybe you need to read the DB using .NET classes and not ADO, so that the blob data type is compatible with .NET.

I'd suggest writing the deserialization code in C#/VB.NET in Visual Studio first. Once you have the code that works, you can port it to TestComplete, or you can compile the .NET code into an assembly/class library and call it from TestComplete via dotNET.

[mugheessiddiqui]

System.Collection.Generic.List included in mscorlib.dll and it is already available in Test Complete.

I think I have to deserialize the object but not sure how to do it.

[AlexKaras]

Hi,

As it was suggested by @HKosova, you should figure-out what is returned from Blob - this may be some string/base64 encoded string/xml/etc. Then you should find corresponding List constructor and use it to deserialize the returning value.

However, as it was also suggested by Helen, it may be easier/more convenient to create a simple .Net assembly with one function that will receive Blob ID and database connection string as input parameters, get Blob from the database, deserialize it and return the list as, say, CrLf-delimited string. I believe that you can easily get the above code from your developers.