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Some scenarios require that a value be is stored in a database column in one form and written to and read from the database column in another form. Servoy supports this requirement with a feature called Column Conversion and called Column Conversion and it has three applications: String Serialization, Blob Serialization and Global Method Conversion.
Servoy also allows the contribution of a column converter by a java plugin.
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Servoy supports object persistence using String Serialization, which involves the conversion of a runtime object into a string format, which can then persist be persisted in a database column. When the column is read from the database, the persistent string will be deserialized back into a runtime object. Because Servoy uses JavaScript as its scripting language, runtime objects will be serialized into standard JSON format.
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Remember that only by assigning an object to a data provider will you actually store the serialized string . You cannot be actually stored. It is not possible to set individual instance properties of an object to directly modify the serialized string. |
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// For Example
my_data_provider.property = 'Foobar'; // This will have no effect on the data provider
// Instead
var obj = my_data_provider; // read the data provider into a runtime object
obj.property = 'Foo Bar'; // Modify the Object's instance properties
my_data_provider = obj; // And reassign it to the data providerdatabaseManager.saveData();
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Blob Serialization
Servoy provides Blob Serialization for persisting an object as a Blob. This involves converting the runtime object into a Blob, which is then persisted in the database column. When retrieving the column data from the database, the Blob is deserialized back into a runtime object.
See code example at String Serialization.
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Blob Serialization can only be used only for column type MEDIA. |
Global Method Conversion
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One can optionally specify the data type of the Object Value. This is useful in situations where the stored value is a different data type than the object value.
Example
The application talks to a database that is storing dates as 8-character text columns to support legacy applications. By setting the Converted Object Type setting to DATETIME, Servoy will treat the column as a date object. Moreover, the two conversion methods written by the developer should assume the Object Value is a Date object.
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