Fields Overview

Usually a field, when inserted in Microsoft Word, already contains an up to date value. For example, if the field is a formula or a page number, it will contain a correct calculated value for the given version of the document. But if you have an application that generates or modifies a document with fields (for example combines two documents or populates with data) then for the document to be useful, all fields should ideally be updated.

A field consists of:

• The field start and separator nodes are used to encompass the content which makes up the field code (normally as plain text)
• The field separator and field end encompass the field result. This can be made up of various types of content ranging from runs of text to paragraphs to tables.
• Some fields may not have a separator which means the entire content makes up the field code.
• The field code defines the behavior of the field and is comprised of the field identifier and often other parameters such as field name and switches.
• The field result contains the most recent evaluation of the field. This value is stored in the field result and is what is displayed to the user. Some fields may not have any field result thus will not display anything in the document. Likewise, some fields may not be updated yet therefore will also have no field result.

Here is a view of how a field is stored in Aspose.Words by using the “DocumentExplorer” example which can be found on Github.

Aspose.Words is a class library designed for server-side processing of Microsoft Word documents and supports fields in the following ways:

• All fields in a document are preserved during open/save and conversions.
• It is possible to update results of some of the most popular fields.

Fields in Microsoft Word

Fields in Microsoft Word documents are complex. There are over 50 field types (each needs its own result calculation procedure), formulas and expressions, bookmarks and references, functions and various switches. Fields can also be nested. Normally when a document is opened, the field result (the value of the field) is shown for all fields in the document. You can toggle the display of field result or field codes in Microsoft Word for all fields by pressing ALT+F9.

Field Code	Field Result

Inserting Fields in Microsoft Word

To insert a field in Microsoft Word:

1. Click on the Insert menu.
2. Click on the Quick Parts drop down menu
3. Select Field
4. You are presented with a screen which allows you to enter the details of the field. On the left side you are given a list of the possible fields and on the right side is a screen to visually edit the properties of the field.
   
5. Additionally you can press the Field Codes button which allows you to directly write out the field code.
   
6. Switches can also be inserted by using the Options button
   
7. Using either method, fill in the desired fields with the appropriate information then press Ok.
8. The field is inserted into the document at the current cursor position.
   

Updating Fields in Microsoft Word

To update a single field in Microsoft Word:

1. Move the caret into the field that you want to update.
2. Press F9 to update the field.

To update all fields in Microsoft Word:

1. Press Ctrl+A to select all the content in the document.
2. Press F9 to update all of the fields found within the selection.

Switching Between Display of Field Code and Field Result

To toggle field codes of a single field in Microsoft Word:

1. Move the caret into the desired field.
2. Press SHIFT+F9 to toggle the field code just for this field.

To toggle field codes of all fields in Microsoft Word:

1. Press ALT+F9

Converting Fields to Static Text in Microsoft Word

To convert a dynamic field to static text in Microsoft Word:

1. Move the caret into the field that you want to convert.
2. Press Ctrl+Shift+F9 to convert the fields to static text.

Removing a Field in Microsoft Word

To remove a field in Microsoft Word:

1. Select the entire content making up the field. If field codes are displayed then the opening and ending braces need to be selected as well.
2. Press Delete to remove the entire field.

Fields in Aspose.Words

When a document is loaded into Aspose.Words, the fields of the document are loaded into the Aspose.Words Document Object Model as a set of separate components (nodes). A single field is loaded as a collection of FieldStart, FieldSeparator and FieldEnd nodes along with the content in between these nodes. If a field does not have a field result then there will be no FieldSeparator node. All of these nodes are always found inline (as children of Paragraph or SmartTag.

The content which makes up the field code is stored as Run nodes between the FieldStart and FieldSeparator. The field result is stored between the FieldSeparator and FieldEnd nodes and can be made up of various types of content. Normally the field result contains just text made up of Run nodes, however it is possible for the FieldEnd node to be located in a completely different paragraph, and thus making the field result comprised of block level nodes such as Table and Paragraph nodes as well.

In Aspose.Words each of the FieldXXX nodes derives from FieldChar. This class provides a property to check the type of field represented by the specified node through the FieldChar.field_type property. For example FieldType.FIELD_MERGE_FIELD represents a merge field in the document.

There are some particular fields that exist in a Word document that are not imported into Aspose.Words as a collection of FieldXXX nodes. For instance, LINK field and INCLUDEPICTURE field are imported into Aspose.Words as a Shape object. This object provides properties to work with the image data normally stored in these fields.

Form fields are also imported into Aspose.Words as their own special class. The FormField class represents a form field in a Word document and provides additional methods that are particular to a form field.

Fields Supported during Update

Calculation of the following fields is supported in the current version of Aspose.Words:

• = (formula field)
• ADDRESSBLOCK
• AUTHOR
• COMPARE
• CREATEDATE
• DATE
• DOCPROPERTY
• DOCVARIABLE
• GREETINGLINE
• IF
• INCLUDETEXT
• MERGEFIELD
• MERGEREC
• MERGESEQ
• NEXT
• NEXTIF
• NUMPAGES
• PAGE
• PAGEREF
• REF
• SECTION
• SECTIONPAGES
• SEQ
• SET
• STYLEREF
• TIME
• TITLE
• TOA
• TOC (including TOT and TOF)
• TC

Sophisticated Parsing

Aspose.Words follows the way Microsoft Word processes fields and as a result it correctly handles:

• Nested fields : IF { =OR({ COMPARE { =2.5 +PRODUCT(3,5 ,8.4) } > 4}, { =2/2 }) } = 1 "Credit not acceptable" "Credit acceptable"
• Field argument can be a result of a nested field.
• Fields can be nested within a field code as well as in the field result.
• Spaces/no spaces, quotes/no quotes, escape characters in fields etc.: MERGEFIELD \f"Text after""Field \n\ame with \" and \\\ and \\\*"\bTextBefor\e
• Fields that span across multiple paragraphs.

Formula Fields

Aspose.Words provides a very serious implementation of the formula engine and supports the following:

• Arithmetic and logical operators: =(54+4*(6-77)-(5))+(-6-5)/4/5
• Functions: =ABS(-01.4)+2.645/(5.6^3.5)+776457 \\\# "#,##0"
• References to bookmarks: =IF(C>4, 5,ABS(A)*.76) +3.85
• Number formatting switches: =00000000 \\\# "$#,##0.00;($#,##0.00)"

The following functions in expressions are supported: ABS, AND, AVERAGE, COUNT, DEFINED, FALSE, IF, INT, MAX, MIN, MOD, NOT, OR, PRODUCT, ROUND, SIGN, SUM, TRUE.

IF and COMPARE Fields

Just some of the IF expressions that Aspose.Words can easily calculate should give you an idea of how powerful this feature is:

• IF 3 > 5.7^4+MAX(4,3) True False
• IF "abcd" > "abc" True False
• IF "?ab*" = "1abdsg" True False
• IF 4 = "2*2" True False
• COMPARE 3+5/34 < 4.6/3/2

DATE and TIME Fields

Aspose.Words supports all date and time formatting switches available in Microsoft Word, some examples are:

• DATE @ "d-MMM-yy"
• DATE @ "d/MM/yyyy h:mm am/pm

Mail Merge Fields

Aspose.Words imposes no limit on the complexity of mail merge fields in your documents and supports nested IF and formula fields and can even calculate the merge field’s name using a formula.

Some examples of mail merge fields that Aspose.Words supports:

• Mail merge field switches: MERGEFIELD FirstName \\\\\\\\* FirstCap \b "Mr. "
• Nested merge fields in a formula: IF { MERGEFIELDValue1 } >= {MERGEFIELD Value2 } True False
• Calculate the name of the merge field at runtime: MERGEFIELD { IF{MERGEFIELDValue1 } >= {MERGEFIELD Value2 } FirstName"LastName" }
• Conditional move to next record in the data source: NEXTIF { MERGEFIELDValue1 } <= { =IF(-2.45 >= 6*{MERGEFIELD Value2 }, 2, -.45) }

Format Switches

A field in a document can have formatting switches that specify how the resulting value should be formatted. Aspose.Words supports the following format switches:

• @ - date and time formatting
• \# - number formatting
• \\\\* Caps
• \\\\* FirstCap
• \\\\* Lower
• \\\\* Upper
• \\\\* CHARFORMAT – format result according to the first character of the field code.
• \\\\* MERGEFORMAT – format result according to how the old result is formatted.

Date and Number Formatting in Fields

When Aspose.Words calculates a field result, it often needs to parse a string into a number or date value and also to format it back to a string.By default Aspose.Words uses the current thread culture to perform parsing and formatting when calculating field values during field update and mail merge. There are also options provided in the form of the FieldOptions class which allows further control over which culture is used during field update.

• By default the FieldOptions.field_update_culture_source property is set to FieldUpdateCultureSource.CURRENT_THREAD which formats fields using the current thread culture.
• This property can be set to FieldUpdateCultureSource.FIELD_CODE so the language set from the field code of the field is used for formatting instead.

Formatting using the Current Thread’s Culture

To control the culture used during field calculation, just use the locale.setlocale method to set the culture of your choice before invoking field calculation. Below example shows how to change the culture used in formatting fields during update.

Using the current culture to format fields allows a system to easily and consistently control how all fields in the document are formatted during field update.

Formatting using the Culture in the Document

On the other hand, Microsoft Word formats each individual field based off the language of the text found in the field (specifically, the runs from the field code). Sometimes during field update this may be the desired behavior, for example if you have globalized documents containing content made up of many different languages and would like each fields to honor the locale used from the text. Aspose.Words also supports this functionality.

The Document class provides a field_options property which contains members which can be used to control how fields are updated within the document. Below example shows how to specify where the culture used for date formatting during field update and mail merge is chosen from.

Finding the Field Code and Field Result

A field which is inserted using DocumentBuilder.insert_field returns a Field object. This is a façade class which provides useful methods to quickly find such properties of a field. Note if you are only looking for the names of merge fields in the document then you can instead use the built-in method MailMerge.get_field_names. Below example shows how to get names of all merge fields in a document.

How to Rename Merge Fields

Below example shows how to rename merge fields in a Word document.