New features
- Interceptors
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We've added an interceptor layer to MetaModel, which makes it possible for you to
intercept operations just before or just after they have been executed. Use-cases of
interceptors are many, but you might need them for migration purposes, for query
rewriting or for logging or security.
Using interceptors you can intercept schemas before they are returned to the user,
queries before they are executed, datasets before they are returned, or update operations
before they are written.
Read the Using interceptors page for examples and more information on interceptors.
- Revised type conversion layer
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We've used the new interceptor layer to implement a type conversion layer which allows you to transparently convert
values of certain column before they are read and written. For instance, you might want to interpret a column in a CSV file
as numbers, even though the column is inherently a string column. With the new type mechanism, that operation is as easy as:
DataContext dc = ...;
dc = Converters.addTypeConverter(dc, column, new StringToIntegerConverter());
Other examples might be to automatically compress and decompress byte arrays, or even serializing and deserializing complete objects to BLOBs.
Read the Automatic type conversion page for examples and more information on type conversion.
- Improved JDBC batch update performance
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The JDBC module's update performance has been greatly improved by using prepared statements as well as committing only once per update.
Since this is completely in line with the semantics of the existing API, the improvement is not something that you will notice in actual
code, but expect a very nice performance improvement (depending on the DB) on execution of large update batches.
Changes to the existing API
- Sanitized the column type transformers feature
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MetaModel has offered conversion of types for a pretty long while, by using the ColumnTypeTransformer class.
But with version 2.2 we've rewritten this layer to be based on the new interceptor mechanism. This means that you
can now do type conversion of any column type and you no longer have to worry about changing the source columns' type to
have this feature.
The ColumnTypeTransformer class has been removed to make place for this new and better implementation of the same concept!
- Removed JDBC "complex query" failover strategy
- We've removed a failover strategy feature from the JDBC module that we did not think was vaiable. The strategy
would handle failing complex queries by falling back to a simple query variant and then use the Query Postprocessor
for further treatment in case of failing complex queries. But an important issue remained, that the "simple failover query"
might be a full table scan, which in case of large tables can be very bad for performance of the whole system. Therefore it was
decided to let these issues fail (since they either way represent a query style that the database will not allow) and not attempt
the failover strategy.
Bugfixes
- Quote escaping in database INSERT statements
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A bug was fixed, which pertained to the generation of INSERT statements and having quotes in the inserted values.
- MongoDB added in MetaModel-full module
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Although MongoDB was officially added in MetaModel 2.1, it was by mistake not included as a dependency in the
MetaModel-full module. It has now been added, so the 'full' maven dependency is easily manageable.
