Posted from Amy’s Sitecore Adventures (a little late)

Breadcrumbs have been covered by just about everyone so there are lots of examples that all seem to do things a Little differently. With that in mind I’m going to keep this short with my example and two other examples I’ve found that might also meet your needs and cover the basics for just about every xslt breadcrumb example you’ll find.

The general idea: you’re at item c, in your tree the path is something like:  /sitecore/content/a/b/c and you want to display a pretty html list for a » b » c anywhere on your site.  You’ll always be dealing with the ancestors of your current item so you’ll be making use of $sc_currentitem/ancestor-or-self::… somewhere.

You’ll need to go through each ancestor item and display it, probably checking to see if you’re at the last item so you don’t display a ‘»’ after the final item. You also need to make sure to not display unwanted ancestors in your breadcrumb, being /sitecore and /content in our case.

So onto the examples!

First is the Sitecore breadcrumb xslt example: http://sdn.sitecore.net/Articles/XSL/Breadcrumb%20Example.aspx
  You will need a login to sdn to view this, but the magic is that it does a for-each across ancestor-or-self::item and then has an if statement to make sure that position()> 2 (this avoids the sitecore/content portion) and avoiding folders and there is the requisite check for position()!=last() so that we do not have the extra » after c.

Next up is Brian Pedreson’s breadcrumb example http://briancaos.wordpress.com/2009/02/09/breadcrumb-in-sitecore/
Similar to the above, however in this case he only selected items which had the appropriate template and a check to make sure the items should be in the navigation at all:
select="$sc_currentitem/ancestor-or-self::item[sc:IsItemOfType('mypages',.) and sc:fld('ShowInMenu',.)='1']"

I am certain there are many many more breadcrumb examples, but these were the first I was able to find easily to share.

Finally, my contribution to the breadcrumb party:

  <xsl:template match="*" mode="main">
    <div>
      <ul class="breadcrumb">
        <xsl:variable name="ancestors" select="$sc_currentitem/ancestor-or-self::item[ancestor-or-self::item/@template='home page']" />
        <xsl:for-each select="$ancestors">
          <li>
            <xsl:choose>
              <xsl:when test="position()=last()">
                <sc:text field="Breadcrumb Title" />
              </xsl:when>
              <xsl:otherwise>
                <sc:link>
                  <sc:text field="Breadcrumb Title" />
                </sc:link>  »
              </xsl:otherwise>
            </xsl:choose>
          </li>
        </xsl:for-each>
      </ul>
    </div>
  </xsl:template>

To satisfy the condition of not showing /sitecore or /content, I am only grabbing ancestors (or self) who have the ancestor (or is the item) that has the special template for the Home item. This excludes anything above the home item, but includes the home item too so that it can be listed. And we end up with a » b » c.

Hope this can be helpful if you are getting started with breadcrumbs!

For each of the properties in your template you can set a source for it, this isn’t always used but can improve user experience drastically when done throughout a site. The source field comes in to play whenever you are using any of the following fields: Droplink, Droplist, Droptree, File, Grouped Droplink, Grouped Droplist, Image, Multilist, Treelist, Rich text field and a number of others.

There are various ways of setting these up to achieve different results – but in general you are using the source to limit the set of items that can be used, and this requirement can also help you determine what kind of field to use. For example, if you have a Set of items all split down into sub folders and want the content editor to make use of the tree, you could use a TreeList or Drop Tree, but if you just want a set of items without the opportunity to see where those items are – multilists or droplinks are the way to go. For Images you’re generally just specifying where to look for and put the images within the media library, and for Rich text fields the source determines the type of editor to use (if not the default).

There are a number of options for setting the source property but not all can work with every field.

Setting the Root Node: To do this you just give the full path to the item you want to use as the ‘root’. This works with just about every field that pulls options and you can easily grab the path from the content pane when you select your desired item(looking at the Item Path). Ie: if you have a treelist and you only want to show the categories item and its children, you’d put in the path to that item: /sitecore/content/Data/Categories

Sitecore Query: This applies to a smaller set of fields (the List Fields), but gives a lot of power and is what I’ll mainly be going over. The fields you can use this with are: Checklist, Droplink, Droplist, Grouped Droplist, Grouped Droplink, or Multilist. You can also use the fast query: this has some limitations over just using sitecore query but gives benefits of better performance and using less memory.

Treelists are also a little special and can use parameters(I think some other fields will work with this as well, but I most often end up using the query on other items so I don’t have a ton of experience with this), you can specify the root item, what templates/items to display or ignore and which they can select, for example:

DataSource=/Sitecore/Content/Home/Root/Node&IncludeTemplatesForSelection=desiredTemplate1,desiredTemplate2&ExcludeTemplatesForDisplay=secretFolder&ExcludeItemsForDisplay=secretItem&AllowMultipleSelection=true

The above sets the root node to /Sitecore/Content/Home/Root/Node and allows the user to select items using desiredTemplate1 or desiredTemplate2, it also excludes secretFolder and secretItem from showing up in the list as well as allowing the user to choose more than one of the same item.

More on Sitecore Query

Using the query option over simply setting a root node improves the experience for your clients as well as helps to keep your data accurate. If you don’t want them to be able to pick a certain template or value or need to select something dependent on a specific axes – using sitecore query will make it possible.

In the source field, your queries need to begin with query: followed by your query. I’m going to go over a few examples I’ve found useful, but for a more detailed explanation of using Sitecore Query take a look at the Data Definition Reference, there is a Sitecore Query section that explains all the details!

So, a few useful tidbits:

* grabs all the children of a node: query:/sitecore/content/home/dessert/*  <--  the * grabs every child and / followed by text denotes the exact item name you’re looking at. So you could also mix this up a bit and return query:/sitecore/home/*/pie/* <-- this will grab all the items that have a parent pie from any item under home with the pie grandchild.

. references the context item, this can be handy if you need to find the ancestors, children or anything along the axes (if you need just the parent, use: .. ): query:./pies/* <-- if we were the dessert item, this would grab all the grandchildren with the parent pie.

// is the descendant axis – this should be used Very sparingly but can be done the following way: query:/sitecore/content/home//pie/* <-- this grabs all the items with a parent pie under home. So that would include, home/pie/*, home/anything/pie/* and so on. The fear with using this is that you’re going to return the whole tree or a whole section which might have thousands of items, so when considering using the descendant axis or any query, be mindful of the result set you will get.

@ denotes a field, and @@ denotes an xml attribute for the item, you’ll probably be using mainly @@templatename or @@templateid.

For example: query:/sitecore/content/home/dessert/*[@pastry=’1’] <-- this grabs all the items under desserts which have the checkbox ‘pastry’ checked (so it might return pies).

Sitecore query also supports the xpath axes, allowing you to use things like ancestor-or-self, following and preceeding (siblings) and so on:

query:./ancestor-or-self::*[@@templatename='Site']/Data/Touts/*

For a more practical example in a multisite solution, the above takes the current item, finds an ancestor or itself that represents the top ‘site’ item and then find the Data folder and then grabs all the children of the Touts folder.

Logical operators can be used to combine options as well, so we could look for query:./*[@@templatename='template1' or @@templatename='template2'] or something more like query:./pies/*|./cakes/* <-- this would give both children of pies and cakes instead of choosing one or the other.

There are also functions you can use (here’s a link with a listing of a number of useful functions), primarily I end up using: position(), last(), and contains()

To use them, you’d do something like query:./*[position()=1] <-- grabs the first item

query:./*[position()=last()] <-- grabs the last item

query:./*[contains(@ingredients,’apple’)] <-- grabs the items with ‘apple’ in their ingredients field, this could also be written as: query:./*[@ingredients = '%apple%']

To test out any query, you can always open up the developer center and then open the xpath builder. You do not need query: before your query but you do need to include fast: if you want to use the fast query.

These queries can become pretty complex depending on your needs, but that initial work can leave content editors with a very easy to use and understand set of items and fields. Leave a comment if you know of any good query examples or are wondering how to form a query to meet your needs (I’ll try to help)!

Reddit had a 6 hour downtime that was caused by them running a database backed by Amazon's cloud disk storage product (EBS Elastic Block Store), but EBS is both unreliable and doesn't flush writes to disk when told to.  This led to corrupted data and disagreements between the master database and slave databases, causing the slaves to not be usable while the master was down. 

Modern SQL databases are not written to work right on hardware that does not have a reliable flush to disk operation. Correct functioning of a modern database absolutely requires that "write back" caching can be shut off, so that if a disk reports a write succeeded that the write actually succeeded.  See for example http://www.postgresql.org/docs/current/static/wal-reliability.html ; this is not at all unique to postgres, I believe that every sql database requires committed writes to actually commit to disk.

The law of leaky abstractions says that as we virtualize more we can do things that appear to work but don't really actually truly work exactly how we think they do, and Murphy says it will hit us with public downtime.

Row ID #770 - Bob submits article about puppies.  Master says it commits, so data is sent to slaves.  Master lied, data was actually in a cache somewhere, write later actually fails in the master - but succeeded in the slaves.

Row ID #770 - John submits article about kittens.  Master now has kittens, slaves have puppies, dogs and cats living together mass hysteria reddit is down for 6 hours migrating master data to new hardware and manually hacking up rebuilt slave tables. 

I don't know how this works with nosql systems and eventual consistency.  Is cassandra ok to run on ebs disks but postgres not at all?  Reddit says their solution is they are going to move to using local ec2 disks; is that actually a solution, or does it just make hitting the problem less likely because ec2 local disks are more reliable than ebs?  Do they still do write back caching?

Meanwhile, Netflix has pointed out that they have actually moved most of their functionality into the cloud.  Specifically, most everything that scales with customers and streaming usage is now served from clouds (although movies come from CDNs, not Amazon's EC2.)

Netflix has posted some really interesting information about the testing they did on EC2: http://perfcap.blogspot.com/2011/03/understanding-and-using-amazon-ebs.html

And their lessons learned is a great place to start when considering working in the cloud at scale: Netflix 5 Lessons We’ve Learned Using AWS

The upshot is, scaling by working in the cloud leads to a whole new set of challenges.  You have to invest more in writing your software to handle hardware failure, you have to test failure scenarios more, you may have to go so far as to redesign network protocols to be less chatty because you have unpredictable latency from shared systems, and you have to expect problems from when abstractions leak as layers of complexity are added to what used to be a simple operation like “write this to disk”.  If you’re at the point where your hardware costs from scaling exceed your software development costs, or if you truly need to be able to handle rapid customer growth faster than you can expand traditional data center use, it can make a lot of sense to tackle these challenges.  But it’s not a no-brainer no-effort proposition – development and testing are going to get harder to handle new scenarios as you switch to using a larger quantity of less reliable resources.

Reddit's explanation:

http://blog.reddit.com/2011/03/why-reddit-was-down-for-6-of-last-24.html

Netflix uses simpledb, hadoop, and cassandra.

http://nosql.mypopescu.com/post/2981945438/why-netflix-picked-amazon-simpledb-hadoop-hbase-and

http://techblog.netflix.com/2011/01/nosql-at-netflix.html

-David

A while back I wrote to ArkeGlobal about windows 7 blocking my files.  It really should go here, so here it is with some updates.

 Original Sept 10, 2009

I downloaded an external dll source for a web application and adding the reference to my project yielded this error:

“System.Security.SecurityException: Request for the permission of type 'System.Web.AspNetHostingPermission, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.”

As it turns out Windows 7 security was blocking my downloaded dlls from running as a trusted source.  Going into the file system itself, I checked the permissions on the actually dll file and a message at the bottom says:

“This file came from another computer and might be blocked to help protect this computer.”

There is an ‘Unblock’ button right next to it and once I clicked it, it solved my issue.

Updated Oct 27, 2009

Since then, I ran into a similar issue but because of the way I had to build the project, every time it ran, it re-added that security back onto those dlls, so I found this: http://www.petri.co.il/unblock-files-windows-vista.htm

Look at solution 3 and/or 4.

 Updated Mar 2011

This last encounter is for those of you that have large, and I do mean large files to copy down.  I had a particular instance where I had to download an upgrade zip file for DNN to lay over a pre-existing one.  When I downloaded and extracted all the contents of it to the client's machine, I had some blocked files.  I grumbled and unblocked it, tried again and got the same error.  Then I realized, Windows had blocked *every* file inside that zip.  I immediately started googling and every single article basically said, 'window's does not provide a way to unblock in bulk'.  So I stared at over 1700 files I had to right-click and unblock by hand with no one providing a solution.  I was about 1 hour in when I had an idea: 

"Right-click -> Properties" on the ZIP folder

It will have the same 'unblock' feature that all it's children are inheriting from.  Once I unblocked the zip, I extracted and all my files played nice again.