pkg.Assert panics when its condition is false, so pkg.Assert(true,
"目前只支持mysql数据库") is a no-op. On postgres or sqlserver the code
generator did not report that it needs MySQL: DBTables returned an empty
list with a nil error, and DBColumns ran its query on the zero-value
*gorm.DB left over from the branch that never assigned, which is a nil
dereference rather than a message.
Assert the driver up front instead of asserting a constant in an else,
which also removes the placeholder *gorm.DB the fall-through relied on.
DBColumns.GetPage had no guard at all and gets the same one.
pkg.Assert panics when its condition is false, so
Assert(TableName == "", "table name cannot be empty") rejected every
request that carried a table name and let the empty one through. The
model layer repeated the inversion with if TableName != "" { return
error }, so either one alone was enough to break the endpoint.
Flip both, and hoist the model guard out of the mysql branch so it
matches GetList ten lines below, which had it right all along.
zhangwenjian