Model design question

I have a class Document that uploads a document. I have a class MetaData that is the name for some metadata for that document. Since a MetaData can have one or more values, there is another class called MetaDataValue that has a ForeignKey to MetaData. Finally, there is a class DocumentMetaDataValue that links these three tables. It almost works...but in the Admin screen when I want to add something to the DocumentMetaData class I can select one or more documents from a drop down list (good!), and one or more Metadata from a dropdown list (good), and I can select one or more MetaDataValues from a drop down list (good). However, the bad news is that the relationship between the MetaData and MetaDataValue is not preserved.

For example, say I have MetaData 'people' with values John, Mark, Allison, and 'events' with values birthday, wedding, funeral. When I add a DocumentMetaData, I want to select 'people' from the MetaData dropdown, and then only the MetaDataValues for 'people' should be displayed in the MetaDataValues dropdown. Instead, what I get is all the MetaDataValues regardless of the associated MetaData, and I can add a MetaDataValue of John to a document under the Metadata label of 'events'. What am I missing in the relationship between the MetaDataValues class and the MetaData class?

These are my classes. I have removed some of the extraneous fields and methods in the classes for clarity.

class MetaData(models.Model):

    metadata_id = models.AutoField(primary_key = True)

    name = models.CharField('metadata name', max_length=200)

    

class MetaDataValue(models.Model):

    metadata = models.ForeignKey(MetaData, on_delete=models.CASCADE,)

    value = models.CharField('value', max_length=200)

                

class Document(models.Model):

    document_id = models.AutoField(primary_key=True)

    title = models.CharField('title', max_length=200)

class DocumentMetaData(models.Model):

    document = models.ManyToManyField(Document)

    metadata = models.ManyToManyField(MetaData)

    metadatavalue = models.ManyToManyField(MetaDataValue)

Thanks!

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