public final class SchemaReport

What Session.schemaReport() found when it compared the registered mappings with the tables that already exist. Reading it changes nothing in the database.

Every difference is one of three kinds, because they call for different fixes:

• Kind.MIGRATION_REQUIRED: the mapping is fine, the schema is behind it – a table or column is missing. A migration brings the database to the mapping.
• Kind.UNSUPPORTED: the existing column cannot hold what the mapping would write, or a key the mapping does not know identifies the rows. Data would be misread or refused, so the mapping has to change – a different storage type, @Temporal for a native timestamp, an explicit @Column name – or the column has to be converted deliberately.
• Kind.CONSTRAINT_MISMATCH: a column’s nullability differs from the mapping. Rows still read and write, but the database accepts a null the mapping cannot hold, or refuses one it can. A schema that is deliberately stricter than the mapping is legitimate, which is why this is kept apart.

SchemaReport report = session.schemaReport();
for (SchemaReport.Issue issue : report.getIssues()) {
    Log.p(issue.getKind() + " " + issue.getTable() + "." + issue.getColumn()
            + ": " + issue.getMessage());
}