Data Table Smart Copy

The Data Table Smart Copy operation is used to merge data from one (source) Data Table with the data in another (target) data table. It's called "Smart" for a reason - it's not just a fancy name. Let's say you have a property "Clients Allowed" on a given context (such as "AccessControl", to use a fictional context). For this specific context, the variable is of a binary type - can be either Yes (allow clients) or No (don't allow).

Now, let's say you have another context, such as "OfficePrinter" (again, just saying). This context also has a property called ClientsAllowed. Only this time, it's an integer describing the number of clients which may connect to this printer or poll it. It's not a binary value. But it has the same name! (As can often happen in a diverse, open system.)

So, if the default Iotellect Server copy operation just took properties and copied them around based on name only, trouble would soon ensue. We needed a "smart" way of copying property values around without breaking the system, and thus Data Table Smart Copy was developed.

Generally speaking, the Data Table Copy operation does its best to copy as much data as possible from the source table to the target table, but always ensures that the target table keeps its original format.

For example, if the format definition of the target table specifies that maximum number of records is 5, the table will contain 5 records after the copy operation, even it there were 100 records in the source table.

Another example: if both the source and target table contain a field called "value", but it's a String type in the source table and an Integer type in the target table, the copy operation will not change the field type in the target table. Instead, it will try to convert all strings from the source field to integers and write them to the target table.

The copy operation is not aborted if errors when copying some record or field. Instead, the operation continues and does its best to copy as much data as it can. Any errors are reported upon completion.

The copy process selects one of the following methods:

• Copy with Key Fields
• Copy without Key Fields

A key field is a field or set of fields of a table which together form a unique identifier for a record (a table entry). The aggregate of these fields is usually referred to simply as "the key".

The first method is selected if the format of the target Data Table defines a non-zero number of key fields. When there's no key field, the second method is used.

With both methods, the system ensures that the number of records in the target table does not exceed minimum and maximum values (defined by the format of Variable Definition).

If the Destination table has Key Fields which aren't defined as Key Fields in the Source table, operation falls back to the copy without key fields method.

The copy operation is divided into three stages. Every stage operates with the records that have identical values in all Key Fields in both tables (the combined value of all key fields can be referred to as a "key").

1. All records in the target table that contain keys not appearing in the source table are deleted.

2. Data from every record of the source table is copied into the record of the target table with the same key, if one exists.

3. For every remaining record of the source table, a new record is created in the target table and data from the source record is copied into the new record.

Sequence of records in destination table is not changed during the Copy with Key Fields process. All records with keys missing in the destination table will be added to the end of destination table regardless of their positions in the source table.

This method also has three stages.

1. If number of records in the target table is greater than in the source table, last records from the target table are deleted to make the number of records equal.

2. Every record of source table is copied to the record of the target table with the same number.

3. If number of records in the Source table is greater than in the Target table, new records are created in the Target table to make the number equal. Data from the Source record is copied into the new record with the same number.

When copying a source record (a single row in a table) to a destination record, each field in the row is tested to see if it can be copied:

1. If field is declared as read-only in the format of target record, it is skipped

2. If field is declared as non-replicable in the format of source of target record, it is skipped

3. If field has the same type in the source and target records, its value is copied directly

4. If field has different types in source and target records, Iotellect Server does its best to convert the value. For example, all types of values can be converted to String, String values can sometimes be converted to Integers, etc.

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