How to extract the schema of an Access (.mdb) database?

Question

I am trying to extract the schema of an .mdb database, so that I can recreate the database elsewhere.

How can I pull off something like this?

Answer 1

You can use the ACE/Jet OLE DB Provider and an ADO Connection object's OpenSchema method to get schema information as a Recordset (which is arguable better than a Collection because it can be filtered, sorted, etc).

The basic methodology is to use adSchemaTables to get the base tables (not VIEWs), then use each TABLE_NAME to fetch adSchemaColumns for ORDINAL_POSITION, !DATA_TYPE, !IS_NULLABLE, !COLUMN_HASDEFAULT, !COLUMN_DEFAULT, !CHARACTER_MAXIMUM_LENGTH, !NUMERIC_PRECISION,!NUMERIC_SCALE.

adSchemaPrimaryKeys is straightforward. adSchemaIndexes is where you will find UNIQUE constraints, not sure wether these can be distinguished from unique indexes, also the names of FOREIGN KEYs to plug into the adSchemaForeignKeys rowset e.g. (pseudo code):

rsFK.Filter = "FK_NAME = '" & !INDEX_NAME & "'") 

-- watch for the gotcha that Jet 3.51 allows a FK based on a nameless PK (!!)

Names of Validation Rules and CHECK constraints can be found in the adSchemaTableConstraints rowset, using the table name in the OpenSchema call, then use the name in the call to the adSchemaCheckConstraints rowset, filter for CONSTRAINT_TYPE = 'CHECK' (a gotcha is a constraint named 'ValidationRule' + Chr$(0), so best to escape the null characters form the name). Remember that ACE/Jet Validation rules can be either row-level or table-level (CHECK constraints are always table-level), so you may need to use the table name in the filter: for adSchemaTableConstraints is [].[].ValidationRule will be [].ValidationRule in adSchemaCheckConstraints. Another gotcha (suspected bug) is that the Field is 255 characters wide, so any Validation Rule/CHECK constraint definition of more than 255 characters will have a NULL value.

adSchemaViews, for Access Query objects based on non-paramaterized SELECT SQL DML, is straightforward; you can use the VIEW name in adSchemaColumns to get the column details.

PROCEDURES are in adSchemaProcedures, being all other flavours of Access Query objects including parameterized SELECT DML; for the latter I prefer to replace the PARAMETERS syntax with CREATE PROCEDURE PROCEDURE_NAME in the PROCEDURE_DEFINITION. Don't boterh looking in the adSchemaProcedureParameters, you won't find anything: the parameters can be enumerated by using an ADOX Catalog object to return an ADO Command e.g. (pseudo code):

Set Command = Catalog.Procedures(PROCEDURE_NAME).Command

then enumerate the Comm.Parameters collection for the .Name, .Type for DATA_TYPE, (.Attributes And adParamNullable) for IS_NULLABLE, .Value for COLUMN_HASDEFAULT and COLUMN_DEFAULT, .Size, .Precision, .NumericScale.

For ACE/Jet-specific properties such as Unicode compression you need to use another kind of object. For example, a Long Integer Autonumber in Access-speak can be found using an ADO Catalog object e.g. (pseudo code):

bIsAutoincrement = Catalog.Tables(TABLE_NAME).Columns(COLUMN_NAME).Properties("Autoincrement").Value

Good luck :)