16.6.11. Customizing DBDoc Model Reporting Templates

This document aims to provide an overview of creating and modifying DBDoc Model Reporting templates, as used by MySQL Workbench.

The MySQL Workbench DBDoc Model Reporting system is based on the Google Template System. This document does not attempt to explain the Google Template System in detail. The Google document How To Use the Google Template System provides a useful overview of how the Google Template System works.

The templates employed by the DBDoc Model Reporting system are text files that contain Markers. These text files are processed by the template system built into MySQL Workbench, and the markers replaced by actual data. The output files are then generated. It is these output files, typically HTML or text, that are then viewed by the user.

Markers can be of six types:

  1. Template Include

  2. Comment

  3. Set delimiter

  4. Pragma

  5. Variable

  6. Section start and Section end

The last two are the most commonly used in MySQL Workbench templates and these important markers will be briefly described in the following sections.

  1. Variables

    The use of variables in the templates is straightforward. Any variables denoted by markers in the template file, will be replaced by their corresponding data, prior to the output file being generated. The mapping between variables and their corresponding data is stored by MySQL Workbench in what is known as a Data Dictionary. In the data dictionary the variable name is the key and the variable's corresponding data is the value. The data dicionaries are built by MySQL Workbench and filled with the data contained in the model being processed.

    By way of example, the following code snippet shows part of a template file:

    Total number of Schemata: {{SCHEMA_COUNT}}

    In the generated output file the variable {{SCHEMA_COUNT}} will be replaced by the number of schemata in the model:

    Total number of Schemata: 2

    A variable can appear as many times as required in the template file.

  2. Sections

    Sections are used to perform iteration in the templates. When MySQL Workbench exchanges the variables in a section for data it will do so iteratively, using all data in the data dictionary in which the variable is defined. MySQL Workbench builds the data dictionaries according to the model currently being processed.

    Again, this is best illustrated by example:

    {{#SCHEMATA}}
    Schema: {{SCHEMA_NAME}}
    {{/SCHEMATA}}

    In the previous code snippet the section start is indicated by the {{#SCHEMATA}} marker. The end of the section is indicated by the {{/SCHEMATA}} marker. When the template is processed, MySQL Workbench will note the section and iterate the section until the variable data for {{SCHEMA_NAME}} in the corresponding data dictionary is exhausted. For example, if the model being processed contains two schemata, the output for the section might resemble the following:

    Schema: Airlines
    Schema: Airports

    That is, the model contains two schemata, Airlines and Airports.

Data Dictionaries

It is important to understand the relationship between sections and data dictionaries in more detail. In a data dictionary the key for a variable is the variable name, a marker. The variable value is the variable's data. The entry for a section in a data dictionary is different. For a section entry in a data dictionary, the key is the section name, the marker. However, the value associated with the key is a list of data dictionaries. In MySQL Workbench each section is usually associated with a data dictionary. You can think of a section as activating its associated dictionary (or dictionaries).

When a template is processed, data dictionaries are loaded in a hierarchical pattern, forming a tree of data dictionaries. This is illustrated by the following table.

Data DictionaryLoads Data Dictionary
MAINSCHEMATA
SCHEMATATABLES, COLUMNS (Detailed is true), FOREIGN_KEYS (Detailed is true), INDICES (Detailed is true)
TABLESREL_LISTING, INDICES_LISTING, COLUMNS_LISTING, TABLE_COMMENT_LISTING, DDL_LISTING
COLUMNS_LISTINGCOLUMNS (Detailed is false)
REL_LISTINGREL (Detailed is false)
INDICES_LISTINGINDICES (Detailed is false)

The root of the tree is the main dictionary. Additional dictionaries are then loaded from the root to form the dictionary tree.

Note

If a template has no sections in it, then any variables used in the template will be looked up in the main dictionary. If a variable is not found in the main dictionary (which can be thought of as associated with the default, or main, section) then no data will be generated in the output file for that marker.

Evaluation of variables

The tree structure of the data dictionaries is important when it comes to evaluation of variables. As variables are defined in data dictionaries, their associated value only has meaning when that particular data dictionary is active, and that means when the section associated with that data dictionary is active. When a variable lookup occurs, the system will check the data dictionary associated with the current section. If the variable value can be found there the replacement is made. However, if the variable's value is not found in the current data dictionary then the parent data dictionary will be checked for the variable's value and so on up the tree until the main data dictionary, or root, is reached.

This can best be illustrated by an example. Assume we want to display the names of all columns in a model. Consider the following template as an attempt to achieve this:

    Report
    ------
    Column Name: {{COLUMN_NAME}}
  

This template will produce no output, even for a model that contains many columns. In this example the only data dictionary active is the main dictionary. COLUMN_NAME however is stored in the COLUMNS data dictionary, which is associated with the COLUMNS section.

With this knowledge the template can be improved as follows:

    Report
    ------
    {{#COLUMNS}}
    Column Name: {{COLUMN_NAME}}
    {{/COLUMNS}}
  

This still does not produce output. Referring to the table Data Dictionary Hierarchy Tree explains why. The COLUMNS data dictionary has the parent dictionary COLUMNS_LISTING. COLUMNS_LISTING has the parent TABLES, which has the parent SCHEMATA, whose parent is the main dictionary. Remember that for a dictionary to be involved in variable lookup, its associated section must currently be active.

So to achieve the desired output we would need the template to be something like the following:

    Report
    ------

    {{#SCHEMATA}}
    {{#TABLES}}
    {{#COLUMNS_LISTING}}
    {{#COLUMNS}}
    Column Name: {{COLUMN_NAME}}
    {{/COLUMNS}}
    {{/COLUMNS_LISTING}}
    {{/TABLES}}
    {{/SCHEMATA}}

  

The following template is the same, but with explanatory comments added:

    Report
    ------

    {{! Main dictionary active}}
    {{#SCHEMATA}}  {{! SCHEMATA dictionary active}}
    {{#TABLES}}  {{! TABLES dictionary active}}
    {{#COLUMNS_LISTING}} {{! COLUMNS_LISTING dictionary active}}
    {{#COLUMNS}}  {{! COLUMNS dictionary active}}
    Column Name: {{COLUMN_NAME}} {{! COLUMN_NAME variable is looked-up, and found, in COLUMNS data dictionary}}
    {{/COLUMNS}}
    {{/COLUMNS_LISTING}}
    {{/TABLES}}
    {{/SCHEMATA}}

  

Imagine now that for each column name displayed you also wanted to display its corresponding schema name, the template would look like this:

    Report
    ------

    {{#SCHEMATA}}
    {{#TABLES}}
    {{#COLUMNS_LISTING}}
    {{#COLUMNS}}
    Schema Name: {{SCHEMA_NAME}} Column Name: {{COLUMN_NAME}}
    {{/COLUMNS}}
    {{/COLUMNS_LISTING}}
    {{/TABLES}}
    {{/SCHEMATA}}

  

When variable lookup is performed for SCHEMA_NAME the COLUMNS dictionary will be checked. As the variable is not found there the parent dictionary will be checked, COLUMNS_LISTING, and so on until the variable is eventually found, where it is held, in the SCHEMATA dictionary.

If there are multiple schemata in the model the outer section will be iterated over a matching number of times, and SCHEMA_NAME will accordingly have the correct value on each iteration.

It's important to always consider which dictionary needs to be active (and which parents) for a variable to be evaluated correctly. In the following section you will find a table that helps you identify section requirements.

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