culled-info.lyx

#LyX 1.6.1 created this file. For more info see http://www.lyx.org/
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\author "" 
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\begin_layout Standard
This document holds some of the sections that we've removed from the book
 so that they don't just disappear into the ether...
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\begin_layout Section
Defining Custom Field Types in Record
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LatexCommand label
name "sub:Defining-Custom-Field-types-record"

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\begin_layout Standard
Similar to the example in section 
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LatexCommand ref
reference "sub:Defining-Custom-Field-types-mapper"

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, when using Record we would like a DecimalField to represent decimal currency
 amounts.
 Our implementation starts off looking very similar to the Mapper version,
 as shown in listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:DecimalField-constructors"

\end_inset

.
 The main difference so far is that the owner type has to be a subtype of
 Record instead of Mapper.
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inline false
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\begin_inset Caption

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DecimalField Constructors
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LatexCommand label
name "lst:DecimalField-constructors"

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class DecimalField[OwnerType <: Record[OwnerType]]
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    (rec : OwnerType, scale : Int)
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    extends Field[BigDecimal,OwnerType] {
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  def this(rec : OwnerType, newVal : BigDecimal) = {
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    this(rec, newVal.scale)
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    set(newVal)
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  }
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  var rounding = RoundingMode.HALF_EVEN
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\begin_layout Standard
The next step is to start defining the methods that are left abstract on
 Field.
 Our first set deals with some basic housekeeping and presentation layer
 details, shown in listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:DecimalField-Methods"

\end_inset

.
 The defaultValue method simply defines the value that we use for new instances.
 The owner method lets Record know which Record instance owns this field.
 asXHtml and toForm define the methods for display and form generation,
 respectively.
 We use the setFromString method (defined later in this section) to handle
 form setting, which keeps the logic clean.
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\begin_layout Standard
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inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
DecimalField Methods
\begin_inset CommandInset label
LatexCommand label
name "lst:DecimalField-Methods"

\end_inset


\end_layout

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\begin_layout Plain Layout

def defaultValue = (new BigDecimal("0")).setScale(scale)
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def owner = rec
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def asXHtml = Text(value.toString)
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\begin_layout Plain Layout

def toForm = text(value.toString, this.setFromString) 
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\end_inset


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\begin_layout Standard
Our final set of methods deals with setting the value of the field, shown
 in listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:DecimalField-Set-Methods"

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.
 The setFromAny method, and its counterpart setFromString, have replaced
 the buildSet...
 method functionality that we would define in Mapper
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status open

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Is that correct?
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.
 setFromAny essentially defers to setFromString for all operations, and
 the only special handling we need is for Lists, Options and Boxes.
 setFromString is required to catch any exceptions thrown during conversion;
 if we have a failure we need to return an Empty as well as calling couldNotSetV
alue to set a flag for validation.
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\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
DecimalField Set Methods
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LatexCommand label
name "lst:DecimalField-Set-Methods"

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\begin_layout Plain Layout

def setFromAny (in : Any) : Box[BigDecimal] =
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  in match {
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    case n :: _ => setFromString(n.toString)
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    case Some(n) => setFromString(n.toString)
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    case Full(n) => setFromString(n.toString)
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    case None | Empty | Failure(_, _, _) | null => setFromString("0")
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    case n => setFromString(n.toString)
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  }
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def setFromString (in : String) : Box[BigDecimal] = {
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  try {
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    Full(this.setAll(new BigDecimal(in)))
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  } catch {
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    case e : Exception => couldNotSetValue; Empty
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  }
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}
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/** Set the value along with proper scale and rounding */
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protected def setAll (in : BigDecimal) = set(in.setScale(scale,rounding))
 
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\begin_layout Standard
Since BigDecimal takes a string as a constructor (in fact, this is the recommend
ed way to initialize it to avoid precision issues with numerics), the setFromStr
ing method is relatively easy to implement.
 To make things even simpler, we add the setAll method that takes a BigDecimal
 as input and then sets the proper scale and rounding on it.
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\begin_layout Standard
\begin_inset Note Note
status open

\begin_layout Plain Layout
Confirm change in behavior from Mapper to not save the original value
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