iCalendar “Field” list (for database schema based on iCalendar standard)

Question

my application has to deal with calendar information (incl. single occurrence, recurrence, etc.). In order to easily interface with other applications I thought that it woul

Answer 1

I've done this (for VEvents only, not supporting TODO items or Journal entires or anything like that). My implementation looks like this (after removing columns that are not specific to the question):

-- One table for each event.  An event may have multiple rRules.
Create Table [vEvent]
    (vEventID Integer Identity(1, 1) Not Null
     Constraint [vEvent.pk]
     Primary Key
     Clustered
    ,title nVarChar(200) Not Null);

-- One table for rRules.
-- My application does NOT support the "bySetPos" rule, so that is not included.
Create Table [rRule]
    (rRuleID Integer Identity(1, 1) Not Null
     Constraint [rRule.pk]
     Primary Key
     Clustered
    ,vEventID Integer Not Null
     Constraint [fk.vEvent.rRules]
     Foreign Key
     References [vEvent] (vEventID)
     On Update Cascade
     On Delete Cascade
    ,[class]            varChar(  12) Not Null Default('public')
    ,[created]         DateTime       Not Null Default(getUTCDate())
    ,[description]     nVarChar(max)      Null
    ,[dtStart]         DateTime       Not Null
    ,[dtEnd]           DateTime           Null
    ,[duration]         varChar(  20)     Null
    ,[geoLat]          Float              Null
    ,[geoLng]          Float              Null
    ,[lastModified]    DateTime       Not Null Default(getUTCDate())
    ,[location]        nVarChar(max)      Null
    ,[organizerCN]     nVarChar(  50)     Null
    ,[organizerMailTo] nVarChar( 100)     Null
    ,[seq]             Integer        Not Null Default(0)
    ,[status]           varChar(   9) Not Null Default('confirmed')
    ,[summary]         nVarChar(  75)     Null
    ,[transparent]     Bit            Not Null Default(0)
    ,[freq]             varChar(   8) Not Null Default('daily')
    ,[until]           DateTime           Null
    ,[count]           Integer            Null
    ,[interval]        Integer        Not Null Default(1)
    ,[bySecond]         varChar( 170)     Null
    ,[byMinute]         varChar( 170)     Null
    ,[byHour]           varChar(  61)     Null
    ,[byDay]            varChar(  35)     Null
    ,[byMonthDay]       varChar( 200)     Null
    ,[byYearDay]        varChar(3078)     Null
    ,[byWeekNo]         varChar( 353)     Null
    ,[byMonth]          varChar(  29)     Null
    ,[wkSt]             Char   (   2)     Null Default('mo'));

-- Class must be one of "Confidential", "Private", or "Public"
Alter Table [rRule]
Add Constraint [rRule.ck.Class]
Check ([class] In ('confidential', 'private', 'public'));

-- Start date must come before End date
Alter Table [rRule]
Add Constraint [rRule.ck.dtStart]
Check ([dtEnd] Is Null Or [dtStart] <= [dtEnd]);

-- dtEnd and duration may not both be present
Alter Table [rRule]
Add Constraint [rRule.ck.duration]
Check (Not ([dtEnd] Is Not Null And [duration] Is Not Null));

-- Check valid values for [freq]. Note that 'single' is NOT in the RFC;
-- it is an optimization for my particular iCalendar calculation engine.
-- I use it as a clue that this pattern has only a single date (dtStart),
-- and there is no need to perform extra calculations on it.
Alter Table [rRule]
Add Constraint [rRule.ck.freq]
Check ([freq] In
    ('yearly'
    ,'monthly'
    ,'weekly'
    ,'daily'
    ,'hourly'
    ,'minutely'
    ,'secondly'
    ,'single')); -- Single is NOT part of the spec!

-- If there is a latitude, there must be a longitude, and vice versa.
Alter Table [rRule]
Add Constraint [rRule.ck.geo]
Check (([geoLat] Is Null And [geoLng] Is Null)
       Or ([geoLat] Is Not Null And [geoLng] Is Not Null));

-- Interval must be positive.
Alter Table [rRule]
Add Constraint [rRule.ck.interval]
Check ([interval] > 0);

-- Status has a set of defined values.
Alter Table [rRule]
Add Constraint [rRule.ck.status]
Check ([status] In ('cancelled', 'confirmed', 'tentative'));

-- Until and Count may not coexist in the same rule.
Alter Table [rRule]
Add Constraint [rRule.ck.until and count]
Check (Not ([until] Is Not Null And [count] Is Not Null));


-- One table for exceptions to rRules.  In my application, this covers both
-- exDate and rDate.  I do NOT support extended rule logic here;  The RFC says
-- you should support the same sort of date calculations here as are supported
-- in rRules: exceptions can recur, etc.  I don't do that; mine is simply a
-- set of dates that are either "exceptions" (dates which don't appear, even
-- if the rule otherwise says they should) or "extras" (dates which do appear,
-- even if the rule otherwise wouldn't include them).  This has proved
-- sufficient for my application, and something that can be exported into a
-- valid iCalendar file--even if I can't import an iCalendar file that makes
-- use of recurring rules for exceptions to recurring rules.
Create Table [exDate]
    (exDateID Integer Identity(1, 1) Not Null
     Constraint [exDate.pk]
     Primary Key
     Clustered
    ,rRuleID Integer Not Null
     Constraint [fk.rRule.exDates]
     Foreign Key
     References [rRule] (rRuleID)
     On Update Cascade
     On Delete Cascade
    ,[date] DateTime Not Null
    ,[type] varChar(6) Not Null);  -- Type = "exDate" or "rDate" for me; YMMV.

To go along with this, I have several SQL Server 2005+ CLR functions that can be used to calculate the dates for various events. I have found the following forms to be very useful:

Select * From dbo.getDatesByVEventID(@id, @startDate, @endDate)
Select * From dbo.getEventsByDateRange(@startDate, @endDate, @maxCount)

Implementation of the above is darn fun to figure out!