Model Driven PowerApp how to write or execute query among entities?

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Hi All, I have one question about the model-driven power app. I know before loading a data source as an entity, there is a tool called power query which can support joint queries among tables. But I don't know if there is a way to write or execute queries among entities, which means after I loaded several entities, I would like to write or execute queries among those entities. I've tried the relationship properties and play around the one-to-many, many-to-one relation, but what I've done is displaying a lookup view or related data grid instead of writing queries. I have seen several demos based on the canvas-driven app that it supports you writing a query inside a text input and based on the flow you set, it can retrieve data from data sources. My question is how to achieve it in a model-driven power app?