Interface IDataTypeComparerService

Compares two values, determining if they are equal, less than, or greater than each other.

This function is designed to handle a wide range of data types, offering flexibility in comparison strategies based on the type and content of the values provided. It supports basic types directly and offers a mechanism for comparing custom data types through converters and comparers.

• For boolean values and other types where comparison beyond equality doesn't apply, it returns Equal or NotEqual.
• For numeric and string values, it returns Equals, LessThan, or GreaterThan.
• When types are mismatched or unsupported, it returns Undetermined. Exceptions may be thrown for invalid values or when necessary conversions fail.
• Null values are treated specially, returning Equals if both are null, or Undetermined otherwise.

When using data types that you know don't naturally work with the above, we recommend running them through the DataTypeConversionService first to change their data type and lookup key to something that does.

let convertedResult = services.dataTypeConverterService.convert(value, LookupKey.Integer);
if (convertedResult.failed)
   return ComparisonResult.Undetermined;
let comparisonResult = services.dataTypeComparerService.compare(convertedResult.value, 5, LookupKey.Integer, null);
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Condition objects

Many Condition objects use this compare() function, such as RangeCondition, EqualToValueCondition, etc. They have these properties on their Config objects to provide conversion prior to comparision:

• conversionLookupKey
• secondConversionLookupKey

Some good examples of using conversionLookupKey and secondConversionLookupKey are:

• case insensitive matching (LookupKey.CaseInsensitive)
• rounding a number to an integer (LookupKey.Integer)
• just the Day or Month or any other number in a Date object (LookupKey.Day, LookupKey.Month)
• a calculated value derived from the value, like the total days represented by a Date object (LookupKey.TotalDays)

Comparison process

Comparison is performed as follows:

1. Checks for a custom DataTypeComparer for the given values. This is rare but allows for specialized comparison logic.
2. Utilizes a default comparer for strings and numbers, converting values as needed. Throws an exception if conversion fails.
3. When provided, lookup keys influence comparison by specifying how to interpret the values (e.g., comparing only the month of a date). If keys differ, attempts are made to align them through conversion before comparing.

Configuring with DataTypeComparers are DataTypeConverters

• The system is preconfigured to handle numbers and strings using a default comparer and booleans with the BooleanComparer. Create your own IDataTypeComparer for custom data types if the conversion solution below is not sufficient.
• Register IDataTypeConverter instances with the DataTypeConverterService to handle conversions between custom data types and base types, and between lookup keys, such as LookupKey.Date to LookupKey.Month with a custom DataTypeConverter.
• When you introduce a LookupKey that you know is compatible with another, register it with the LookupKeyFallbackService. We've preregistered all numeric lookup keys to fall back to LookupKey.Number and all string lookup keys to fall back to LookupKey.String. The compare() function will use this service to align lookup keys before comparing.

Returns a comparer that supports both values or null if not.