Inserting a row to the AssetImages table fails in the "test/-asset.spec.ts" test

You can run the command below to make the error.

```
NODE_ENV=test yarn mocha --exit -r ts-node/register --timeout 60000 --recursive test/api/asset.spec.ts
```

Here is the log from the Postgresql when you run the command above.

```
2019-11-18 17:00:42.129 KST [72847] ERROR: insert or update on table "AssetImages" violates foreign key constraint "AssetImages_assetType_fkey"
2019-11-18 17:00:42.129 KST [72847] DETAIL: Key (assetType)=(b03745e7296053068a1ac475b377656574b394d3) is not present in table "AssetSchemes".
```

Run NODE_ENV=test yarn mocha --exit -r ts-node/register --timeout 60000 --recursive test/api/asset.spec.ts and inspect test/api/asset.spec.ts first. Trace the AssetImages insert and the AssetImages_assetType_fkey relationship to AssetSchemes; done means the test no longer fails with the reported PostgreSQL foreign-key error.

索引モデルが issue の本文から書いたものです。