This wraps AcDbJoinEntityPE::joinEntity, which when implemented for an Entity, it can be used to join two supported entities together. Some implementations might require the this and the secondary entity be of the same type, while other implementations might convert the data from the secondary entity to match the type of the this entity.

Public Function JoinEntity(
    secondaryEntity As Entity
) As void

public void JoinEntity(
    Entity secondaryEntity
);

<![CDATA[Database db = Application.DocumentManager.MdiActiveDocument.Database; Autodesk.AutoCAD.DatabaseServices.TransactionManager tm = db.TransactionManager; 

using (Transaction t = tm.StartTransaction()) { try { Line pLine1 = new Line(new Point3d(0, 0, 0), new Point3d(1, 1, 0)); Line pLine2 = new Line(new Point3d(1, 1, 0), new Point3d(2, 2, 0)); 

// Join the second line to the first line pLine1.JoinEntity(pLine2); } catch (Autodesk.AutoCAD.Runtime.Exception e) { Application.DocumentManager.MdiActiveDocument.Editor.WriteMessage("nJoin error: "); Application.DocumentManager.MdiActiveDocument.Editor.WriteMessage(e.ErrorStatus.ToString()); } t.Commit(); }]]>