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oData multilevel entity with self reference?

Hi Experts,

I have a flat list of products which are in basicly a product hierarchy. So each entry in the table has an id and parent id, while the parent id can point to an id of a different entry in the table. What i now want to achieve is to build a oData which can expand the whole tree while the level of deepenes is unknown and respond with a nested json that represents the hierarchy.

So i have built the oData with one entity (product list) and have defined association from the entity to it self by mapping id to parent id with an 1:M association. I also have created a Navigation Property which points to the association.

Now i started to overwrite the GET_EXPANDED_ENTITYSET method. What i want to achieve is, that whenever the oData is called with the url /sap/opu/odata/sap/ZORG_TEST_SRV/PRODAREASet?$expand=PRODAREAS&$format=json it responds with a nested json that shows the complete hierarchy, all levels.

Now i am wondering how to build the hierachy inside the method, beause the generated structure in mpc class does not have any table for child nodes.

i tried to built a local type (product), a table type of my local type and the local type that includes the table of itself but this seem not to work. I have also tried a class instead of structure but then copy_data_to_ref call inside GET_EXPANDED_ENTITYSET gave me an error that ref are not allowed.

Is this use case even possible with oData if you do not know how deep your structure can be? Basicly i need an "expand all" with unknown deepness for an entity that self references 1:n


Thank you and Best Regards


Dimitri

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1 Answer

  • Best Answer
    Posted on Oct 18, 2018 at 04:21 PM

    You have to explicitly specify how many levels you want to expand, e.g.

    GET PRODAREASet?$expand=PRODAREAS,PRODAREAS/PRODAREAS,PRODAREAS/PRODAREAS/PRODAREAS

    to expand three levels deep.

    OData V4 adds a shortcut

    GET PRODAREASet?$expand=PRODAREAS($levels=3)

    and even allows

    GET PRODAREASet?$expand=PRODAREAS($levels=max)

    to request the maximum number of levels supported by the service (which is allowed to defend itself against DOS attacks by interpreting "max" appropriately :-)

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