Template Syntax - Part 1 of 2 Leave feedback

Note

This article is the first part of the Template Syntax series of articles. For second part, please visit Template Syntax - Part 2 of 2.

A typical template for GroupDocs.Assembly Engine is composed of common document contents and tags that describe the template’s structure and data bindings. You can form these tags using just running text that can occupy multiple paragraphs to be more descriptive.

A tag body must meet the following requirements:

• A tag body must be surrounded by “<<” and “>>” character sequences.
• A tag body must contain only text nodes.
• A tag body must not be located inside markup document nodes.

A tag body typically consists of the following elements:

• A tag name
• An expression surrounded by brackets
• A set of switches available for the tag, each of which is preceded by the “-” character

<<tag_name [expression] -switch1 -switch2 ...>>

An optional comment can be written to provide a human-readable explanation.

<<tag_name [expression] –switch1 –switch2 ... // optional_comment >>

Warning

The optional comment feature is supported by version 19.1 or greater

Particular tags can have additional elements. Some tags require closing counterparts. A closing tag has the “/” character that precedes its name. This tag’s name must match to the name of the corresponding opening tag.

<</tag_name>>

Note: Tag body elements are case-sensitive.

The following table describes lexical tokens that you can use in template expressions and restrictions on these tokens’ usage comparing with C# Language Specification 5.0.

You can use the following identifiers that are not preceded by a member access operator in template expressions:

• The name of a passed data source object
• The name of an iteration variable within its scope (see Outputting Sequential Data for more information)
• The name of a lambda function parameter within the scope of the lambda function
• A fully or partially qualified name of a type that is known by the engine (see Setting up Known External Types for more information)
• The name of a member of an object that is determined as follows:
  • Inside a data band body, the object is resolved to the innermost iteration variable.
  • Outside a data band body, the object is resolved to a passed data source.

The feature of the omitting of an object identifier while accessing the object’s members is also known as the contextual object member access. See Using Contextual Object Member Access for more information.

GroupDocs.Assembly Engine enables you to use external visible types in template expressions. A visible type is a public type with outer types (if any) are public as well. You can use a data source object of any visible type to pass it to the engine.

However, you can use the identifier of a visible type in template expressions only if the following additional requirements are met:

• The type is not void.
• The type does not represent an array.
• The type is not an open or closed generic type.

Note: Whereas using of generic types’ identifiers is forbidden in template expressions, you can use identifiers of nullable types in the shorthand "T?" form.

Also, the engine enables you to use anonymous types in template expressions. Such types are useful while composing expressions with grouping by multiple keys. See Enumeration Extension Methods for the examples.

GroupDocs.Assembly Engine enables you to access the following public (static and instance) members of accessible types in template expressions:

• Fields
• Properties
• Indexer getters
• Methods
• Constructors

However, you can use a functional type member in template expressions only if the following additional requirements are met:

• The functional member returns a value.
• The functional member does not have ref or out parameters.
• The functional member does not take generic type arguments.

The engine supports the following features when dealing with functional members:

• Overload resolution according to C# Language Specification 5.0
• Using of default parameter values without support of named parameters
• Using of parameters taking a variable number of arguments

GroupDocs.Assembly Engine enables you to use the following built-in extension methods in template expressions:

• Extension methods mimicking the ones for IEnumerable<T> (see Enumeration Extension Methods for more information)
• Extension methods for iteration variables (see Extension Methods of Iteration Variables for more information)

Note: Extension methods, other than the built-in ones, can be used only in the form of plain static methods in template expressions.

The following list contains predefined and user-defined operators that Document Assembler enables you to use in template expressions.

• Primary:

  x.y f(x) a[x] new x?.y a?[x]  
  

• Unary:

  - ! ~ (T)x
  

• Binary:

  * / % + - << >> < > <= >= == != & ^ | && || ??
  

• Ternary:

  ?:
  

The engine follows operator precedence, associativity and overload resolution rules declared at C# Language Specification 5.0 while evaluating template expressions. But be aware of the following limitations in the behavior comparing with the specification:

• Implicit user-defined conversions are supported only when specified explicitly.
• The indexing of multi-dimensional arrays is not supported.
• Whereas the object initializer syntax is supported (including objects of anonymous types), the collection initializer syntax is not.

Also, the engine enables you to use lifted operators in template expressions.

GroupDocs.Assembly Engine enables you to use lambda functions only as arguments of built-in enumeration extension methods in template expressions. See Enumeration Extension Methods for more information.

Note: Lambda functions declared within template expressions are not interchangeable with delegates. Thus, you can not pass delegates as arguments to built-in enumeration extension methods.

You can use both explicit and implicit lambda function signatures in template expressions. If you do not specify the type of a parameter of a lambda function explicitly, the type is determined implicitly by the engine depending on the type of the corresponding enumeration.

Note

This link will explain you how we utilized the DataSet Objects in Business Layer.

GroupDocs.Assembly Engine enables you to access DataTable objects contained within a particular DataSet instance by table names using the “.” operator in template expressions. That is, for example, given that ds is a DataSet instance that contains a DataTable named “Persons”, you can access the table using the following syntax.

ds.Persons

Note Table names are case-insensitive.

GroupDocs.Assembly Engine enables you to treat DataTable and DataView objects in template expressions as enumerations of their rows. That is, you can use template expressions evaluated to such objects in foreach tags (see Outputting Sequential Data for more information).

Also, you can normally apply enumeration extension methods (see Enumeration Extension Methods for more information) to DataTable and DataView objects in template expressions. For example, given that persons is a DataTable or DataView instance, you can count its rows using the following syntax.

persons.Count()

GroupDocs.Assembly Engine enables you to access a data associated with a particular DataRow or DataRowView instance in template expressions using the “.” operator. The following table describes, which identifiers you can use to access different kinds of the data.

Warning

Field and table names are case-insensitive.

To determine parent-child relationships for a particular DataTable instance, the engine uses DataRelation objects contained within the corresponding DataSet instance. Thus, you can manage these relationships in a common way.

Warning

Instead of using of table names to access data of child or parent rows, you can also use relation names, which is useful when you deal with multiple relations to the same table.

GroupDocs.Assembly Engine enables you to treat IDataReader implementors as enumerations of IDataRecord implementors in template expressions. That is, you can use IDataReader implementors in template expressions in the same way as DataTable objects. See Working with DataTable and DataView Objects for more information.

However, you can not use IDataReader implementors in template expressions in conjunction with enumeration operations that require a caching of enumeration items. The examples of such operations are grouping and sorting. To work around this restriction, use DataTable objects instead.

Document Assembler enables you to access field values of a particular IDataRecord implementor by field names using the “.” operator in template expressions. To use this feature, one of the following conditions must be met:

• The IDataRecord implementor represents an iteration variable upon enumerating an IDataReader implementor (see Outputting Sequential Data for more information).
• The IDataRecord implementor does not implement the IDataReader interface.

The following example shows, how to use this feature. Given that r is an IDataRecord implementor that has a field named “Name”, you can access the field’s value using the following syntax.

r.Name

Note Field names are case-insensitive.

You can insert images to your reports dynamically using image tags. To declare a dynamically inserted image within your template, please follow these steps:

1. Add a textbox to your template at the place where you want an image to be inserted.

2. Set common image attributes such as frame, size, and others for the textbox, making the textbox look like a blank inserted image.

3. Specify an image tag within the textbox using the following syntax.

   <<image [image_expression]>>
   

The expression declared within an image tag is used by the engine to build an image to be inserted. The expression must return a value of one of the following types:

• A byte array containing an image data
• A Stream instance able to read an image data
• An Image object
• A string containing an image URI, path, or Base64-encoded image data

While building a report, the following procedure is applied to an image tag:

• The expression declared within the tag is evaluated and its result is used to form an image.
• The corresponding textbox is filled with this image.
• The tag is removed from the textbox.

Note: If the expression declared within an image tag returns a stream object, then it is closed by the engine as soon as the corresponding image is built.

By default, the assembler stretches an image filling a textbox to the size of the textbox. However, you can change this behavior in the following ways:

• To keep the size of the textbox and stretch the image within bounds of the textbox preserving the ratio of the image, use the keepRatio switch as follows:

  <<image [image_expression] -keepRatio>>
  

• To keep the width of the textbox and change its height preserving the ratio of the image, use the fitHeight switch as follows.

  <<image [image_expression] -fitHeight>>
  

• To keep the height of the textbox and change its width preserving the ratio of the image, use the fitWidth switch as follows.

  <<image [image_expression] -fitWidth>>
  

• To change the size of the textbox according to the size of the image, use the fitSize switch as follows.

  <<image [image_expression] -fitSize>>
  

• To change the size of the textbox according to the size of the image without increasing the size of the textbox, use the fitSizeLim switch as follows.

  <<image [image_expression] -fitSizeLim>>
  

  Warning

  If the size of the image is greater than the size of the textbox, then the fitSizeLim switch acts like fitHeight or fitWidth. Otherwise, the fitSizeLim switch acts like fitSize.

You can insert contents of outer documents to your reports dynamically using doc tags. A doc tag denotes a placeholder within a template for a document to be inserted during runtime.

Syntax of a doc tag is defined as follows.

<<doc [document_expression]>>

Warning

A doc tag can be used almost anywhere in a template document except textboxes and charts.

An expression declared within a doc tag is used by the assembler to load a document to be inserted during runtime. The expression must return a value of one of the following types:

• A byte array containing document data
• A Stream instance able to read document data
• An instance of the Document class
• A string containing a document URI, path, or Base64-encoded document data

While building a report, an expression declared within a doc tag is evaluated and its result is used to load a document which content replaces the doc tag then.

Warning

If an expression declared within a doc tag returns a stream object, then the stream is closed by the assembler as soon as a corresponding document is loaded.

By default, a document being inserted is not checked against template syntax and is not populated with data. However, you can enable this by using a build switch as follows.

<<doc [document_expression] -build>>

When a build switch is used, the assembler treats a document being inserted as a template that can access the following data available at the scope of a corresponding doc tag:

• Data sources
• Variables
• A contextual object 
• Known external types 

You can set checkbox values to either checked or unchecked in your reports dynamically by taking the following steps:

1. Add a checkbox content control to your template at a place where you want it to appear in a result document.
2. By editing content control properties, add a check tag to the title of the checkbox content control using the following syntax.

<<check [conditional_expression]>>

Here, conditional_expression defines a condition upon which the value of the checkbox content control is to be set to checked (or unchecked, if the condition is not met). The conditional expression must return a Boolean value.

While building a report, a conditional expression declared within a check tag is evaluated and the value of its containing checkbox content control is set accordingly. The check tag itself is removed then.

Warning

Dynamic checkbox value setting is available for Word Processing documents only.

You can dynamically add items to comboboxes and dropdown lists defined in your template by taking the following steps:

1. Add a combobox or dropdown list content control to your template at a place where you want it to appear in a result document.
2. By editing content control properties, add an item tag to the title of this content control using the following syntax.

<<item [value_expression] [display_name_expression]>>

Here, value_expression defines a value of a combobox or dropdown list item to be added dynamically. This expression is mandatory and must return a non-empty value.

In turn, display_name_expression defines a display name of the combobox or dropdown list item to be added. This expression is optional. If it is omitted, then during runtime, a value of value_expression is used as a display name as well.

Note – Values of both value_expression and display_name_expression can be of any types. During runtime, Object.ToString() is invoked to get textual representations of these expressions’ values.

While building a report, value_expression and display_name_expression are evaluated and a corresponding combobox or dropdown list item is added. A declaring item tag is removed then.

A single item tag causes addition of a single combobox or dropdown list item during runtime. You can add multiple combobox or dropdown list items using multiple item tags as shown in the following snippet.

<<item ...>><<item ...>>

Also, you can normally use item tags within data bands to add a combobox or dropdown list item per item of a data collection. For example, given that clients is a DataTable instance having a field named “Name”, you can use the following template to cover such a scenario.

<<foreach [client in clients]>><<item [client.Name]>><</foreach>>

An item tag can also be combined with an if tag to add a combobox or dropdown list item depending on a condition as shown in the following snippet.

<<if ...>><<item ...>><</if>>

Existing combobox and dropdown list items are not affected by item tags. Thus, you can combine both ways of adding combobox and dropdown list items using a template: static and dynamic.

Note – While inserting a combobox or dropdown list, Microsoft Word adds a default item that has to be removed manually, if the item is unwanted.

Using GroupDocs.Assembly, you can insert hyperlinks to URI or Bookmarks to your reports dynamically using link tags. The syntax of a link tag is defined below for various types of documents:

<<link [uri_or_bookmark_expression][display_text_expression]>>

If the insertion of the link to cell A1 is required:

<<link ["A1"] ["Home"]>>

<<link ["Slide1"] ["Home"]>>

You can make your templates less cumbersome using the contextual object member access feature. This feature enables you to access members of some objects without specifying the objects’ identifiers in template expressions. An object to which the feature can be applied is determined depending on a context as follows:

• Inside a data band body, the object is resolved to the innermost iteration variable.
• Outside a data band body, the object is resolved to a passed data source.

Obviously, inside a data band body, you can not use the feature to access members of an outer iteration variable or a passed data source object. With the exception of this restriction, you can use both contextual and common object member access syntaxes interchangeably depending on your needs and preferences.

Consider the following example. Given that ds is a DataSet instance containing a DataTable object named “Persons” that has fields named “Name” and “Age”, you can use the following template to list the contents of the table.

Alternatively, you can use the following template involving the contextual object member access syntax to get the same results.

You can use different document blocks to represent the same data depending on a condition with the help of conditional blocks. A conditional block represents a set of template options, each of which is bound with a conditional expression. At runtime, these conditional expressions are sequentially evaluated, until an expression that returns true is reached. Then, the conditional block is replaced with the corresponding template option populated with data.
A conditional block can have a default template option that is not bound with a conditional expression. At runtime, this template option is used, when none of conditional expressions return true. If a default template option is missing and none of conditional expressions return true, then the whole conditional block is removed during runtime.

You can use the following syntax to declare a conditional block:

<<if [conditional_expression1]>>
template_option1
<<elseif [conditional_expression2]>>
template_option2
...
<<else>>
default_template_option
<</if>>

Note: A conditional expression must return a Boolean value.

A common conditional block is a conditional block which body starts and ends within paragraphs that belong to a single story or table cell.
If a conditional block belongs to a single paragraph, it can be used as a replacement for an expression tag that involves the ternary “?:” operator. For example, given that items is an enumeration, you can use the following template to represent the count of elements in the enumeration:

You have chosen <<if [!items.Any()]>>no items<<else>><<[items.Count()]>> item(s)<</if>>.

Note: A template option of a common conditional block can be composed of multiple paragraphs, if needed.

You can normally use common conditional blocks within data bands. For example, given that items is an enumeration of the strings “item1”, “item2”, and “item3”, you can use the following template to enumerate them and apply different formatting for even and odd elements:

<<foreach \[item in items\]>><<if \[IndexOf() % 2 == 0\]>><<\[item\]>>  
<<else>><<\[item\]>>  
<</if>><</foreach>>

In this case, the engine produces a report as follows:

item1
item2
item3

You can use data bands within common conditional blocks as well. For example, given the previous declaration of items, you can check whether the enumeration contains any elements before outputting their list:

<<if [!items.Any()]>>No data.
<<else>><<foreach [item in items]>><<[item]>>
<</foreach>><</if>>

A table-row conditional block is a conditional block which body occupies single or multiple rows of a single document table. The body of such a block (as well as the body of its every template option) starts at the beginning of the first occupied row and ends at the end of the last occupied row as follows:
Note: Table rows occupied by different template options in the following template are highlighted with different colors.

public class Client
{
    public String Name { get { ... } }
    public String Country { get { ... } }
    public String LocalAddress { get { ... } }
    ...
}

Using table-row conditional blocks, you can pick to output a single row among several rows of a single document table depending on a condition like in the following example:

Note

Note: You can use common conditional blocks within table-row data bands as well.

Also, you can use data bands inside table-row conditional blocks. For example, you can provide an alternate content for an empty table-row data band using the following template:

Note

Note: If tags denoting boundaries of a template option are contained within a single table cell, the option is considered to be a common template option, rather than a table-row one. That is, the option is considered to occupy contents within the cell, rather than the whole row. That is why, a single-cell alternate content in the previous example is located between an opening if and else tags, rather than between an else and closing if tags.