This tutorial is intended to be a conversation with newbies to Dabo. Please check the Dabo wiki for more information and other tutorials.
Let me say what this is not. It is not a tutorial on Python , installation of Databases, or the use of SQL. I have to assume you understand the syntax of Python and SQL. And you will follow the install instructions provided by your favorite database. I will make an effort not use any thing to advanced and I'm sure the code will be easy to read even for a laymen. OK let's start with some background. Dabo's primary goal is to provide an easy way to create a desktop application and most desktop applications require persistent data. In that light Dabo supports several database engines. SQLite, MySQL, MS-SQL, FireBird, and my favorite Postgres. However, Dabo does not provide the actual interfaces to access the database engines. The developer is expected to download and install the python interfaces to the database of choice. Please check the http://dabodev.com/wiki/FrontPage for instructions on where to find the required files. For example if you are using Postgres you will need psycopg2. The wiki provides the link to http://initd.org/tracker/psycopg/wiki/PsycopgTwo where you will find the required files. I highly recommend that you test your setup by connecting with the database and retrieving some data. That way you know your setup works and therefore you would expect Dabo to work too. I know some reader will be thinking that their favorite database is better than my choice. I don't disagree nor do I agree. It's just that I have had great success with Postgres and it is the database I'm using for this tutorial. However, everything thing I'll be showing should apply to any of the databases supported. In it's basic form Dabo database support is agnostic. But rest assured that Dabo can support your favorite databases advance features too. Dabo is a 3 tier framework. The User Interface, Business Rules, and the Database. We will be working with “bizObjects”. What is a 'bizObject” you ask? There is a very good explanation on the wiki FAQ – http://dabodev.com/wiki/FAQs#Bizobj. I like to think of it in simple terms. It's the code that allows me to create, save, and delete data using my UI. The “bizObject” provides validation and understands my data (business rules?). A simple but very powerful concept. So to support the bizObject we need to supply a few things, a connection to a database, a description of the table, and any rules we want enforced. The Connection: All the python interfaces Dabo uses are suppose to comply with DB-API 2.0. That means there is a standard way to access the database. Here's the link http://www.python.org/dev/peps/pep-0249/ if you need to check it out. If you do read it there is a section on “connection” and you come to realize that what is passed for the connection parameter is not defined. It (the parameters) depends on what is required by the database engine. So Dabo needs you to supply those parameters before it can make a connection to your database. Right off the bat let me say the easiest way to setup a connection is to use the “CxnEditor.py” app. It works and and is a great example of Dabo eating it's own dog food (CxnEditor was created using Dabo). I use it for my projects and if there was a better way - I'd use it. But it really does not do much (all the real work is done in the framework). CxnEditor creates a XML file that contains the parameters required by the python connection interface that applies to your database. Like user name, password, host, database name or anything else that is needed to allow a database connection. It makes sense that we will need a connection before we start asking for data from the database. But where do you put the code and what does the code look like. When you are hand coding a form you will create something similar to the following: class MainForm(dabo.ui.dForm): def afterInit(self): #place some UI code here self.layout() if __name__ == "__main__": app = dabo.dApp() app.BasePrefKey = "fileTutor" app.setAppInfo("appName", "File Tutorial ") app.MainFormClass = MainForm app.start() And in the “class MainForm” (our entry point) you will need to add a method “createBizobjs”. This is where you will add your connection instructions and add descriptions of bizObjects. To start we add the connection information as follows: #this method uses the cnxml file created by CxnEditor def createBizobjs(self): self.Application.addConnectFile("FileName.cnxml") # FileName = the name created with the CxnEditor.py # This call will actually create the connection if it hasn't already # been made. If it has, it returns the existing connection, so that # multiple connections aren't used up. self.connection = self.Application.getConnectionByName("connectionName") Don't let the two names "FileName.cnxml" and "connectionName" confuse you. The "connectionName" is the name of the connection within the file "FileName.cnxml". It is possible to have more than one connection name within the same file but that is beyond this tutorial. So “self.connection” is the actual connection we will be providing to our bizObjects. Remember, that is what really is allowing our program to talk to the database. When ever Dabo needs to communicate with the database it uses the “self.connection” object. For those of you that need to know how to create a “self.connection” without using the CxnEditor here it is: from dConnectInfo import dConnectInfo connInterface = dConnectInfo(DbType=”Postgres”) connInterface.Host = "192.168.1.201" connInterface.Database = "DatabaseName" connInterface.User = "john" connInterface.PlainTextPassword = "passWord" self.connection = dConnection(connInterface).getConnection() If your database needs more – such as a port address. Add it – as in connInterface.Port = "5432". But take my advise and use the CxnEditor. It's easy and it works. There maybe some special case where the cnxml file will not meet your needs. But I haven't run into it. So our code looks like: class MainForm(dabo.ui.dForm): def afterInit(self): #place some UI code here self.layout() def createBizobjs(self): self.Application.addConnectFile("FileName.cnxml") # FileName = the name created with the CxnEditor.py # This call will actually create the connection if it hasn't already # been made. If it has, it returns the existing connection, so that # multiple connections aren't used up. self.connection = self.Application.getConnectionByName("connectionName") if __name__ == "__main__": app = dabo.dApp() app.BasePrefKey = "bizObjTutor" app.setAppInfo("appName", "bizObject Tutorial ") app.MainFormClass = MainForm app.start() So far we haven't said much. Only that we need a connection to a database and the bizObjects use it to communicate with the database. But without this information nothing happens and the most powerful Dabo feature is useless. The next installment I'll provide a small form with a UI and we will build our first bizObject. Your job will be to insure that you have your favorite database running and working with python. John Fabiani _______________________________________________ Post Messages to: Dabo-users@leafe.com Subscription Maintenance: http://leafe.com/mailman/listinfo/dabo-users Searchable Archives: http://leafe.com/archives/search/dabo-users This message: http://leafe.com/archives/byMID/dabo-users/[EMAIL PROTECTED]
