android - GreenDao is it possible to do a To-Many relation in only one direction? -

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let's have ingredient entity, , recipe entity. lots of recipes might refer same ingredient. 

recipe 1 uses ingredients 1, 2 , 3 recipe 2 uses ingredients 1, 3 , 5

i want able load ingredients recipe, not reverse.

i think need model many-to-many relation creating separate entity track recipe <-> ingredient mappings.

is understanding correct, or there way make work tomany relation?

i don't think using single tomany relation work, because greendao requires them have foreign key in target entity original entity (see "modelling to-many relations" in docs). means ingredients can refer single recipe - 2 recipes reference same ingredient 1 of them lose relation.

ftr, if don't set foreign key in target entity, tomany relation lost after restarting application (i.e. works current database session). tip: simulate scenario in automated tests, call daosession.clear() before loading object , asserting contains values expect.

since 1 ingredient can part of many recipes , 1 recipe consists of many ingredients relation many-to-many relation.

the common way model in db store relation in separate table.

this independent of use of greendao. achieve model using greendao have create new entity recipetoingredient , build relations using entity.

update

if free in designing database can use schema this:

table ingredienttype -------------------------- id          | integer (pk) description | text  table recipe -------------------------- id          | integer (pk) description | text  table ingredient -------------------------- id_recipe   | integer (fk) id_type     | integer (fk) unit        | text quantity    | integer

this means tomany-relation ingredient recipe , igredient ingredienttype. technically many2many-mapping additional attributes between ingredienttype , recipe.

in greendao use 2 tomany-relations model this.


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