动态查询SQL服务器

Question

I'm working on creating a dashboard. I have started to refactor the application so methods relating to querying the database are generic or dynamic.

I'm fairly new to the concept of generics and still an amateur programmer but I have done some searching and I have tried to come up with a solution. The problem is not really building the query string in a dynamic way. I'm fine with concatenating string literals and variables, I don't really need anything more complex. The bigger issue for me is when I create this query, getting back the data and assigning it to the correct variables in a dynamic way.

Lets say I have a table of defects, another for test cases and another for test runs. I want to create a method that looks something like:

public void QueryDatabase<T>(ref List<T> Entitylist, List<string> Columns, string query) where T: Defect, new()

Now this is not perfect but you get the idea. Not everything about defects, test cases and test runs are the same but, I'm looking for a way to dynamically assign the retrieved columns to its "correct" variable.

If more information is needed I can provide it.

Answer 1

You're re-inventing the wheel. Use an ORM, like Entity Framework or NHibernate. You will find it's much more flexible, and tools like that will continue to evolve over time and add new features and improve performance while you can focus on more important things.

EDIT :
Although I think overall it's important to learn to use tools for something like this (I'm personally a fan of Entity Framework and have used it successfully on several projects now, and used LINQ to SQL before that), it can still be valuable as a learning exercise to understand how to do this. The ORMs I have experience with use XML to define the data model, and use code generation on the XML file to create the class model. LINQ to SQL uses custom attributes on the code-generated classes to define the source table and columns for each class and property, and reflection at run-time to map the data returned from a SqlDataReader to the properties on your class object. Entity Framework can behave differently depending on the version you're using, whether you use the "default" or "POCO" templates, but ultimately does basically the same thing (using reflection to map the database results to properties on your class), it just may or not use custom attributes to determine the mapping. I assume NHibernate does it the same way as well.

Answer 2

You are reinventing the wheel, yes, it's true. You are best advised to use an object-relational mapper off the "shelf". But I think you also deserve an answer to your question: to assign the query results dynamically to the correct properties, you would use reflection. See the documentation for the System.Reflection namespace if you want more information.