UML 101

So you need to read the entire UML book in 20 minutes. What do you do? These are the excerpts from the Unified Modeling Language Reference Manual I was reading and thought I could summarize for a quick refresh.

 

Aggregation and composition:

Generalization:

Kinds of dependencies:

Use case diagram:

Kinds of Use Case relationships:

Activity Diagram:

Sequence diagrams and Activation:

Component Diagram:

Deployment Diagram:

Packages and relationships:

Left outer join in Entity Framework

This evening I heard someone say that Left Outer Joins are not possible in Entity Framework or perhaps Left Outer Joins are possible, but they bring in all the data and then filter out the right table.

I felt an urge to argue, but I resisted. I thought I would investigate before I waste time. I came up with some articles pretty quickly.

1. Left Outer Join in LINQ
2. Left Outer Join using Inverse Navigation Property
3. DefiningQuery Element
4. Left Outer Join in LINQ to SQL
5. LINQ to Entities with Multiple Left Outer Joins

I am sure these should resolve all questions related to Left Outer Joins.

Now about the performance and the question about how the data is brought, I am pretty sure we can prove that LINQ Queries all support deferred execution. But we can always prove that using the SQL Query Profiler.

Hope this helps.

Singleton Vs. Static Class

Well I was asked this question once. “What is a singleton design pattern and why should I use it? Why not use a static class instead?”

And it was quite surprising how it went. I said that Singleton is used when you need to maintain state. Static classes are used when you want to club together a bunch of stateless methods that do something irrespective of which instance calls these methods. Math class is a good example.

So he asked me, can I not maintain state in a static class? So I said if you want to instantiate something in a static class how would you do it? And surprisingly he told me that he would do it in a static constructor. I asked him, is it possible to instantiate anything in the static constructor or even declare an instance type in a static class? And he asked me is it not possible? I said it is not as far as I know and he asked me if I am sure.

Now the way the questions were asked about this subject, I was quite surprised. The interviewer looked quite convinced that instance types can be declared in a static class. I am surprised how he was allowed to take the interview in the first place. Or was he checking my confidence?

I wonder.