Question

When should I change or not change my component GUID in WIX? The Microsoft SDK information is confusing.

Glytzhkof edit: To clarify, the question deals with when a component GUID should be changed for an MSI component. A component can change with aspects such as: changed destination path, addition or removal of files to/from the same component, addition of registry data etc… This causes problems with regards to the so called component referencing, i.e the best practice for creating components in MSI.

Answer 1

The overall concept of MSI is that there is a 1:1 mapping between
a component GUID (unique identifier) and an absolute path
(install location / key path). The full path, including file name if
any (a directory can be the key path for a component). See update below for a new Wix feature to deal auto-magically
with this.

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Rob Mensching (WiX author):

• Windows Installer Component Rules 101
• Windows Installer Components Introduction

More on Component Rules:

• Organizing Applications into Components
• Best Practice for Creating Components.

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I use some simple rules to deal with the overly complex and rather counterintuitive component rules (especially for developers as opposed to deployment specialists):

• Always use a separate component per file (even for non-binaries). This avoids all kinds of problems. There are a few exceptions:
  • Multi-file .NET assemblies should all be in one component since they should always be installed / uninstalled as a single unit.
  • A few other, general file types come in "matching pairs" – they belong together. Often these are content and index files. As an example consider Microsoft help files:
    • .HLP and .CNT files belong together.
    • .CHM and .CHI files belong together.
  • There are likely several such file types that belong together and should hence be put in the same component so they install/uninstall together – I suspect certain certificate files to be candidates. It is hard to come up with a definite list. Simply ask yourself "do these files always belong together" – so they always show up in pairs whenever there is a new version? If yes, then install them via the same component. Set the versioned file, if any, as key file.
  • I want to add driver files as an example of a bunch of files always belonging together: SampleDriver.cat, SampleDriver.inf, SampleDriver.sys, SampleDriver.cer. They must all match as a "unit" for deployment.
• Remember that once you have allocated a GUID for a component, it’s set in stone for that component’s key path (absolute path). If you move the file to a new location or rename the file, give it a new component GUID (since the absolute path is different it’s effectively a new identity).
• In summary component GUIDs are tied to an absolute installation location, and not to a specific file. The GUID doesn’t follow the file around if it moves. The GUID reference counts an absolute location, not the file per se.
• Do not add or remove files from an existing component. All sorts of upgrade and patching problems result. This is why I like one file per component as a general rule.
• There is a lot more to component referencing, but I will leave it at that for an "overview".

Some samples:

• You rename the file C:\Program Files\MyCompany\MyApp\MyFile.exe to C:\Program Files\MyCompany\MyApp\MyFile_NEW.exe. What does this mean for component creation? This is a new absolute installation path, so you generate a new GUID for the hosting component, OR you add a new component and delete the old one (which has the same effect).
• Your updated MSI delivers a new version of MyFile.exe. The location is the same as before, this means the component GUID should not change. It is the same file (identity), just in a different version.

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UPDATE:

Auto Component-GUIDs: WIX now has a new auto-generate component GUID feature that calculates a GUID as long as the target path
stays the same. I have not tried this out to be honest, but many seem
to use it without problems, and Rob Mensching (Wix author) states it is safe for normal use. As a concept I highly recommend this
since it features some auto-magic and shields you from some
complexity.

Minimal WiX Markup: Also note that you can leave out a lot of source attributes from
your Wix xml file and rely on Wix defaults instead of hard
coding values.