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If a tnsnames.ora file is not found, the connection fails. 

6. Set Up Datical Project DbDefs to Use the

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TNS Alias

When you create a DbDef in a project and choose Oracle as the database type, you set the following property:

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See also Configuring Step Settings (DbDefs)#OracleDatabaseStepSettings. 

7. Testing the Connection

See Testing Oracle Connections