Problem

When importing data using the ExcelTemplate class, you can choose to preserve strings or to have ExcelTemplate attempt to convert them to a number. Your choice depends upon how you import the data.

Solution

Excel stores values internally either as strings or numbers. The data you import can be in a variety of formats, including numbers, strings, dates, booleans, etc. ExcelTemplate uses the data type of your data to determine how it should be inserted into the Excel template. However, by default, ExcelTemplate also attempts to convert strings to numbers where appropriate. This article will explain what options are available for controlling this conversion.

Special case: Please note that preserving numbers with leading zeros as strings does not always result in the desired behavior. Special consideration should be taken when importing numbers with leading zeros. For information about the steps that should be taken to best do this, please refer to this post: How to preserve leading zeros with ExcelWriter.

Conversion features

There are two features which control whether the automatic conversion of numeric strings takes place:

1. PreserveStrings property

This property is set to false by default, but setting it to true will disable any automatic conversion of strings to numbers from occurring. Be sure to set this property before calling Process.

For example, if you wanted to disable the conversion of any numbers to strings when importing data, you would set the PreserveStrings property to true:

 xlt.PreserveStrings = true; 

2. Convert and preserve data marker modifiers

The convert and preserve data markers modifiers allow finer control of which values are converted and which are not. Depending on how the PreserveStrings property is set, you can use these modifiers in your template to override the global behavior on certain columns.

For example, if PreserveStrings is set to its default value of false, you could set a specific column to not be converted by putting the Preserve modifier on that column’s data marker.

 %%=MyData.ColumnOfStrings(Preserve) 

Recommended practices

By default, ExcelTemplate will attempt to convert strings to numbers wherever it can. This is desirable when your data is not already stored in objects of the appropriate data type. We generally recommend setting the PreserveStrings property to true, so that this automatic conversion will not occur. It is generally preferrable to use the appropriate object/data types for your data to eliminate the need for any conversion by ExcelWriter. This provides the most predictable behavior when importing data.

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