 Happiness, a new idea in the training of educational actors in education: Knowledge-relationship at the service of a "transformational training" 
The objective of the article is to understand how a happiness engineering device centered on knowledge-relationship allows for « transformational training ». The methodology is based on a survey of semi-structured interviews and on a thematic content analysis of the dissertations. It was conducted with CPE trainees and teacher trainees in the Prevention-Health-Environment course. The results analyze the types of knowledge-relations in the realization of the experimental device by the trainees and the formative dimensions associated with learning in such an engineering.