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The CustomizeDiff functionality in helper/schema is powerful, but directly
writing single CustomizeDiff functions can obscure the intent when a
number of different, orthogonal diff-customization behaviors are required.
This new library provides some building blocks that aim to allow a more
declarative form of CustomizeDiff implementation, by composing a number of
smaller operations. For example:
&schema.Resource{
// ...
CustomizeDiff: customdiff.All(
customdiff.ValidateChange("size", func (old, new, meta interface{}) error {
// If we are increasing "size" then the new value must be
// a multiple of the old value.
if new.(int) <= old.(int) {
return nil
}
if (new.(int) % old.(int)) != 0 {
return fmt.Errorf("new size value must be an integer multiple of old value %d", old.(int))
}
return nil
}),
customdiff.ForceNewIfChange("size", func (old, new, meta interface{}) bool {
// "size" can only increase in-place, so we must create a new resource
// if it is decreased.
return new.(int) < old.(int)
}),
customdiff.ComputedIf("version_id", func (d *schema.ResourceDiff, meta interface{}) bool {
// Any change to "content" causes a new "version_id" to be allocated.
return d.HasChange("content")
}),
),
}
The goal is to allow the various separate operations to be quickly seen
and to ensure that each of them runs independently of the others. These
functions all create closures on the call parameters, so the result is
still just a normal CustomizeDiffFunc and so the helpers in this package
can be combined with hand-written functions as needed.
As we get more experience writing CustomizeDiff functions we may wish to
expand the repertoire of functions here in future; this initial set
attempts to cover some common cases we've seen so far. We may also
investigate some helper functions that are entirely declarative and so
don't take callback functions at all, but want to learn what the relevant
use-cases are before going in too deep here.
61 lines
2.3 KiB
Go
61 lines
2.3 KiB
Go
package customdiff
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import (
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"github.com/hashicorp/terraform/helper/schema"
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)
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// ResourceConditionFunc is a function type that makes a boolean decision based
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// on an entire resource diff.
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type ResourceConditionFunc func(d *schema.ResourceDiff, meta interface{}) bool
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// ValueChangeConditionFunc is a function type that makes a boolean decision
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// by comparing two values.
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type ValueChangeConditionFunc func(old, new, meta interface{}) bool
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// ValueConditionFunc is a function type that makes a boolean decision based
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// on a given value.
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type ValueConditionFunc func(value, meta interface{}) bool
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// If returns a CustomizeDiffFunc that calls the given condition
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// function and then calls the given CustomizeDiffFunc only if the condition
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// function returns true.
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//
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// This can be used to include conditional customizations when composing
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// customizations using All and Sequence, but should generally be used only in
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// simple scenarios. Prefer directly writing a CustomizeDiffFunc containing
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// a conditional branch if the given CustomizeDiffFunc is already a
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// locally-defined function, since this avoids obscuring the control flow.
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func If(cond ResourceConditionFunc, f schema.CustomizeDiffFunc) schema.CustomizeDiffFunc {
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return func(d *schema.ResourceDiff, meta interface{}) error {
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if cond(d, meta) {
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return f(d, meta)
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}
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return nil
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}
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}
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// IfValueChange returns a CustomizeDiffFunc that calls the given condition
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// function with the old and new values of the given key and then calls the
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// given CustomizeDiffFunc only if the condition function returns true.
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func IfValueChange(key string, cond ValueChangeConditionFunc, f schema.CustomizeDiffFunc) schema.CustomizeDiffFunc {
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return func(d *schema.ResourceDiff, meta interface{}) error {
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old, new := d.GetChange(key)
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if cond(old, new, meta) {
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return f(d, meta)
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}
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return nil
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}
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}
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// IfValue returns a CustomizeDiffFunc that calls the given condition
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// function with the new values of the given key and then calls the
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// given CustomizeDiffFunc only if the condition function returns true.
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func IfValue(key string, cond ValueConditionFunc, f schema.CustomizeDiffFunc) schema.CustomizeDiffFunc {
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return func(d *schema.ResourceDiff, meta interface{}) error {
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if cond(d.Get(key), meta) {
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return f(d, meta)
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}
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return nil
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}
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}
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