Dependency Injection Architecture

[Dan_Bev]

Hi to all, I'm studying "Dependency Injection Principles, Practices and Patterns" by Manning.

I want to share with you a simple architecture just to know if I'm on the correct path or I miss something.

Suppose we have a simple program that read CDR (Charging data record) from text file and write them to a DB.

I can assume a code like that


void DoStuff(string filePath)
{
CDRReader cdrReader = new CDRReader(filePath);
CDR cdr = null;
List<CDR> listOfCdrs = new List<CDR>();

while ( (cdr = cdrReader.GetNext()) != null)
{
listOfCdrs.Add(cdr);
}

DBLayer databaseLayer = new DBLayer();
databaseLayer.SaveCdrs(listOfCdrs);
}


Now, I analize the code for introducing DI:

• The core object of all it's the CDR class, a POCO. I think I don't need to extract an interface for this: real implementations need to depends directly by CDR
• Let's concentrate for now only on CDRReader: I assume that I can have in future various way to read from CDR' source (e.g. stored from database). So I think I can extract an interface for this. Moreover, I can assume that I can have different file representations of CDR (plain text, json, xml), so I refactor in this way

void DoStuff(string filePath)
{
iCDRParser cdrParser = new CDRPlainTextParser();
iCDRReader cdrReader = new CDRStreamReader(filePath, cdrParser);
CDR cdr = null;
List<CDR> listOfCdrs = new List<CDR>();

while ( (cdr = cdrReader.GetNext()) != null)
{
listOfCdrs.Add(cdr);
}

//this does not interest me for now
DBLayer databaseLayer = new DBLayer();
databaseLayer.SaveCdrs(listOfCdrs);
}

interface iCDRReader
{
CDR GetNext();
}

class CDRStreamReader : iCDRReader
{
//It depends on Stream has it declare on class name, I think it's correct
StreamReader _stream;
iCdrParser _cdrParser;

public CDRStreamReader(string path, iCDRParser cdrParser)
{
//guard not shown for brevity
_stream = new StreamReader(path);
_cdrParser = cdrParser;
}

public CDR GetNext()
{
//don't care for the example how to dispose stream
string line;
if ( (line = _stream.ReadLine()) == null)
return null;

return _cdrParser.Parse(line);
}

interface iCDRParser
{
CDR Parse(string line);
}

class CDRPlainTextParser : iCDRParser
{
public CDR Parse(string line)
{
CDR cdr = new CDR();
//stuffs here
return cdr;
}
}

And now what torments me:

• It's correct that GetNext() and Parse(string) method return a CDR? I assume that's a POCO, so I think it's an overkill implements an iCDR interface
• On parser's Parse(string) method it's correct the "new CDR()" line? Where should i be able to create CDR objects?
• It's correct parser's Parse(string) signature, forcing a "string" as parameter?

Thanks to all those who will dedicate a few minutes of their time to me

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