Freemarker Design Guide (2)

Design Freemarker Design Guidelines (2)
2. Data Model



(1) Basic



L introduced the three basic object types used in templates in QuickStart: scalars, hashes, and sequences, but there are other capabilities:



Øscalars: Store Single value



Øhashes: acts as a container for other objects, each associated with a unique query name



Øsequences: acts as a container for other objects, in order to access



Ø method: Calculate by passing parameter, return result with new object



Ø user-defined FTL tags: macros and converters



L usually each variable has only one of these capabilities, but a variable can have several of these capabilities, as in the following example:



(Root)



|



+-mouse = "Yerri"



|



+-Age = 12



|



+-color = "Brown" >



L Mouse is both scalars and hashes, merging the data model above into the following template:



${mouse} <#--use mouse as scalar-->



${mouse.age} <#--use mouse as hash-->



${mouse.color} <#--use mouse as hash-->



L Output results are:



Yerri



12



Brown



(2) Scalar variable



L scalar variable store single value, can be:



Ø string: Simple text, enclosed in a template with quotes (either single or double quotes)



Ø numbers: Use numeric values directly in the template



Ø Date: Store date/Time related data, can be date, time or date-time (Timestamp); Typically, date values are added to the data model by programmers, and designers only need to show them



Ø Boolean value: True or FALSE, usually used in < #if ...> tags



(3) Hashes, sequences and collection



L Some variables do not contain anything that can be displayed, but they contain other variables as containers, and there are two types of them:



Øhashes: Has a unique query name associated with each variable it contains



Øsequences: associated with a number and each variable it contains, index value starting from 0



L A collection variable is usually similar to sequences unless its size is inaccessible and the index cannot be used to obtain its child variables; The collection can be viewed as restricted sequences that can only be used by the < #list ...> directives



(4) method



The L method variable is usually based on the given parameter computed value



L The following example assumes that the programmer has placed the method variable avg in the data model to calculate the numeric average:



The average of 3 and 5 is: ${avg (3, 5)}



The average of 6 and is: ${avg (6, 10, 20)}



The average of the price of Python and Elephant are: ${avg (Animals.python.price, Animals.elephant.price)}



(5) Macros and converters



L Macros and converter variables are user-defined directives (custom FTL tags) that describe these advanced features later



(6) Node



The L-node variable is represented as a node in the tree structure, usually used in XML processing, and is described in a later special section