DBCon

property DBCon: TvxDBCon read;

Example

procedure ScriptEvent(var Value: Variant);
var
  Link: TvxDBLink;
  Con: TvxDBCon;
begin
  Value := Null;
  if Source <> nil then
    if Source.DBConCount > 0 then
    begin
      Link := Source.DBCons[0];
      if Link <> nil then
      begin
        Con := Link.DBCon;
        if Con <> nil then
          Value := Con.Database;
      end;
    end;
end;

Usage

DBCon loads on first access and returns the database-connection module configured for this data-definition link.

Failures and value refresh

The getter catches a load exception and logs Error loading DB Connection "<name>", but it does not clean up the object in that exception handler. Consequently:

• a normal unresolved/missing module returns nil;
• an exceptional load can return a non-nil partially initialised/unloaded object;
• the logged error can set the surrounding log/status false even though the exception is not re-raised here; and
• any non-nil result is cached, so later reads do not retry or reload it.

If the normal failure path returns nil, a later access tries again. If configuration changes after a successful cached load, this property still returns the existing object until the owning link/definition is recreated.

Ownership and safe use

Do not free, replace or retain the result beyond the owning execution/definition lifetime. A nil check prevents dereferencing no object but does not prove that a non-nil result loaded successfully, can connect, is authorised or has current credentials. Operations such as transactions, disconnect and writable endpoint/credential fields have the side effects documented on TvxDBCon.

When obtaining the link from DBCons[Index], check the data-definition reference and DBConCount in separate nested tests before indexing. Do not assume Boolean evaluation will protect an unsafe dereference in a combined expression.

Additional Technical Info

DBCon returns the TvxDBCon module referenced by this link, loading it from Velox configuration on first access.

The property is read-only, can return nil and returns a Velox-owned live object rather than a copy.

Getter implementation

When the cached field is nil, the getter:

1. creates a TvxDBCon owned by this TvxDBLink;
2. calls LoadModule with the link's configured connection FID and an empty parent FID;
3. frees/nils the object when loading returns normally but ModuleLoaded is false; and
4. otherwise retains and returns the object for subsequent accesses.

This configuration load can query VxConfig. It does not itself call the connection's target-database ConnectDatabase path; methods/properties on the returned object determine whether target connection/pool work follows.

Performance and concurrency

The first/failed access can perform configuration I/O and logging; cached reads are constant-time. No locking protects the lazy cache. Resolve/use it within one action thread.

Related entries

• TvxDBLink — collection, ownership and lifecycle context.
• TvxDBCon — returned module contract.

Created 2026-07-15