DEX keys and descriptors

Three properties of DEX shape how you write queries here.

An APK contains several dexes

An APK usually holds several classes*.dex. DexSQL puts them all in one set of SQL relations and distinguishes them by file_id. Three rules follow:

Every *_idx index is valid only within one dex. method_idx = 42 is a different method in a different dex. Always include file_id in a join key, or rows from different dexes will be crossed.
One entity appears once per dex that mentions it. A method referenced by 5 dexes has 5 rows in methods. To count entities, use DISTINCT descriptor.
Strings are the exception: their scope is the pool, not the dex. The key is (string_pool_id, string_idx), reached from a file_id via dex_files.string_pool_id. In a DEX 041 container several logical dexes share one pool; before 041 each dex has one pool of its own.

What a descriptor is

A descriptor is the string DEX uses to name an entity, and the most common lookup key in this schema:

entity	form	example
type	`L<package path>;`	`Ljava/lang/String;`
method	`<class><code>-></code><name>(<params…>)<return>`	`Lpkg/Cls;->name(I)V`
field	`<class><code>-></code><name>:<type>`	`Lpkg/Cls;->field:I`

Primitives are single letters: V void, Z boolean, B byte, S short, C char, I int, J long, F float, D double. Arrays take a [ prefix, e.g. [Ljava/lang/String;. Method parameters have no separator between them.

DEX itself stores only type descriptors; method and field descriptors are assembled by DexSQL from those parts.

References vs. definitions

A DEX id section (method_ids, field_ids, type_ids) registers what the current dex references, wherever that entity is defined; the actual member definitions live in class-data, which is separate data. DexSQL preserves the distinction:

relation	one row is
`methods`, `fields`, `types`	one reference
`class_methods`, `class_fields`, `classes`	one definition

A method that is only referenced still appears in methods, with its definition-sourced columns NULL. See the methods entry for the exact behavior of these columns.