DefaultValueStrategy

The default value strategy is one of RedGs most important features, and like most of RedG can be customized to fit your requirements.

The default implementation is DefaultDefaultValueStrategy. It delivers null for any nullable columns and a fixed non-null value for NOT NULL columns. However, most of the time, the DefaultDefaultValueStrategy will not completely meet your needs.

You could easily write your own DefaultValueStrategy from scratch, but we recommend using the DefaultValueStrategyBuilder. It provides a convenient and clear API for creating custom DefaultValueStrategys.

DefaultDefaultValueStrategy

RedG's default default value strategy supports the following data types and provides a fixed default value for them.

Data type	Default value
String	"-" (Oracle does not support empty Strings and treats them as NULL)
char / Character	' ' (whitespace character)
boolean / boolean	false
everything extending Number / primitive number types	0
everything extending java.util.Date	0 (= 01.01.1970)
Java 8 date types	1970-01-01T00:00:00.000Z

If a column is a primary key or has a unique constraint, a value that is unique to that column (but may be the same as in other unique columns) is generated.

Data type	Unique default value	Max number of unique values
String	"A", "B", ..., "Z", "AA", "AB" ...	2^64
char / Character	Unicode Character starting with \u0001 up until \uffff	(2^16)-1 = 65,535
boolean / boolean	false, then true	2
everything extending Number / primitive number types	0, 1, 2, ...	2^64
everything extending java.util.Date	Counting up milliseconds since unix epoch, starting at 0	until year 8099
Java 8 date types	Counting up milliseconds since unix epoch, starting at 0	until year 8099

DefaultValueStrategyBuilder

DefaultValueStrategyBuilder is the recommended way of creating DefaultValueStrategys. It provides a convenient and clear API for creating DefaultValueStrategys.

DefaultValueStrategyBuilder builder = new DefaultValueStrategyBuilder();

builder.whenColumnNameMatches("ID")
        .thenUseProvider(new IncrementingNumberProvider());
builder.whenTableNameMatches(".*CARD").andColumnNameMatches("TYPE")
        .thenUse("MASTERCARD");
builder.when(columnModel -> columnModel.getDbFullTableName().equals("CCM.CREDITCARD.UUID"))
        .thenCompute((columnModel, expectedType) -> UUID.randomUUID().toString());

builder.build();

By default DefaultValueStrategyBuilder will add a DefaultDefaultValueStrategy as fallback value provider. However, you can change this using DefaultValueStrategyBuilder.setFallbackStrategy(DefaultValueStrategy).

PluggableDefaultValueStrategy

This is the DefaultValueStrategy implementation that the DefaultValueStrategyBuilder uses internally.

The PluggableDefaultValueStrategy has a list of PluggableDefaultValueProviders. When a default value needs to be generated, it checks whether a provider can provide a default value for the required data type / table / column. The values from all eligible providers are then collected and the first not-null value is returned as the default value. If no eligible provider is found or all return null, null gets returned. Even if the column is nullable (notNull == false), a not-null value is preferred.

The following providers are bundles with RedG:

Class name	Description
ConstantStringProvider	Provides a constant String which can be set by the user.
ConstantValueProvider	Provides a constant value for a certain data type. Returns the value if value.getClass() equals the exact required type.
StaticNumberProvider	Provides a static number.
IncrementingNumberProvider	Provides an incrementing number. The start value can be specified. The counter is incremented for each column separately. Ideal for index columns.
StaticDateProvider	Takes a java.util.Date as a parameter and returns it for every java date type.
CurrentDateProvider	Returns the current date / time for every java date type.
ConditionalProvider	Encapsulates another provider and will only return its value if the regular expressions for table & column name match.
CustomConditionalProvider	A conditional provider that is even more flexible that the ConditionalProvider. Is used by the builder system.
DefaultDefaultValueProvider	A provider encapsulating the DefaultDefaultValueStrategy. Use for fallback purposes.

Custom provider implementation

Implementing a custom provider is easy. Simply implement the PluggableDefaultValueProvider interface and implement both the getDefaultValue and willProvide method. The willProvide method should return true if getDefaultValue can and should produce a default value for the current column and data type.

Custom implementation

Custom default value strategies have to implement the DefaultValueStrategy interface.

If notNull is true and null is returned, RedG will fail. RedG does not perform further checks on the value generated by this method. You have full control and responsibility.

public interface DefaultValueStrategy {
    <T> T getDefaultValue(ColumnModel columnModel, Class<T> type);
}