Using Variables

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LINQ Reporting Engine enables you to use variables in template documents. Variables are useful when you need to calculate an expensive value just once and access it multiple times in a template. Also, calculation of complex values such as running (progressive) totals may require variables, see “Appendix C. Typical Templates” to get an example.

You can declare a variable in a template using a var tag as follows.

<<var [variable_type variable_name = variable_value]>>

The following table describes elements of the var tag.

Element Optional? Remarks
Variable Type Yes You can specify the type of a variable explicitly. This type must be known by the engine (see “Setting up Known External Types” for more information).
If you do not specify the type explicitly, it is determined implicitly by the engine from the specified variable value.
Variable Name No For a new variable, its name must be a unique identifier.
Assignment Operator No
Variable Value No

During runtime, a var tag is removed while the value of the corresponding variable is calculated and set appropriately.

After a variable is declared in a template, its value can be accessed using the name of the variable as any other identifier. For example, the following template outputs string “Hello!”

<<var [s = “Hello!”]>><<[s]>>

You can redefine the value of a variable using a var tag against the name of this variable. For example, the following template outputs string “Hello, World!”

<<var [s = “Hello, ”]>><<[s]>><<var [s = “World!”]>><<[s]>>

Using of variables has the following restrictions:

  • You can not redefine the type of a variable.
  • You can not use the contextual object member access feature against a variable. See “Using Contextual Object Member Access” for more information.
  • Using a var tag, you can not redefine the value of an iteration variable or a data source.

FAQ

  1. Q: How do I declare a variable with an explicit type in a template?
    A: Include the type before the variable name inside the var tag, e.g. <<var [java.time.LocalDate startDate = DateTime.Now]>. The engine must know the type; you can register custom types via “Setting up Known External Types”.

  2. Q: How can I reference a variable after it has been declared?
    A: Use the variable name inside double‑angle brackets. For example, after <<var [total = 0]>, you can output its value with <<[total]>> anywhere later in the document.

  3. Q: Can I change the type of a variable once it has been created?
    A: No. The variable’s type is fixed at the first declaration and cannot be redefined. Attempting to declare the same name with a different type will cause a runtime error.

  4. Q: Is it possible to redefine a variable’s value inside a foreach loop?
    A: Yes, you may assign a new value to the same variable inside a loop using another var tag, e.g. <<var [sum = sum + item.Price]>>. However, you cannot change the variable’s type or redefine an iteration variable itself.

  5. Q: How do I use a variable to format a date inside a template?
    A: Declare a variable that holds the formatted string, for example: <<var [java.time.format.DateTimeFormatter fmt = java.time.format.DateTimeFormatter.ofPattern("yyyy-MM-dd")]>> then <<var [formattedDate = dateValue.format(fmt)]>>. Output with <<[formattedDate]>>. This avoids repeated formatting calls.

Using Contextual Object Member Access in Java