I ‘ve recently been building a set of reports that all output data in a common format, and also group their data in a common format. Each report needs to be able to have a date predicate based on day, week or month. Using LINQ to LLBL Gen Pro (the ORM tool I’m currently using) I set up a base report class that has abstract methods defining the date predicates and query bodies, but share the grouping and output mechanisms. What allows this is being able to return a LINQ Expression in the methods that define the date predicates.
The abstract date predicates end up looking like the below:
protected abstract Expression<Func<T, bool>> GetDayDatePredicate(int reportBuckets);
Once implemented the date predicate ends up being something like:
protected overrides Expression<Func<dataEntity>,bool>> GetDayDatePredicate(int reportBuckets)
{
return d => d.CreatedDate.Date > DateTime.Now.AddDays(-1 * reportBuckets).Date;
}
Having the predicates in method form serves two purposes: first the method name clearly states what the predicate is doing, (fairly straightforward above but bucketing by weeks is not nearly as clear), and second it allows the base class to create the query by doing something like the below:
public void RunQuery(int numberOfBuckets, IQueryable<T> q)
{
Expression<Func<T, bool>> datePred = GetDayDatePredicate(numberOfBuckets);
q = q.where(datePred);
RunQuery(q);
}
This allows a base class to manage running several reports if they all have similar structure. When adding a report I just add a new implementation of the base class and fill in the abstract bits and then I know I have a report that our UI can use, since it relies on the common output the base class enforces on its children. Don’t know if it’s all that good a solution, we’ll see.