Category: SAP

entity MainEntity: cuid, managed {
    file            : Association to Files @mandatory  @assert.target;
}

entity Files : cuid, managed {
    content         : LargeBinary @stream  @Core.MediaType: mediaType  @Core.ContentDisposition.Filename: fileName  @Core.ContentDisposition.Type: 'inline'; 
    mediaType       : String      @Core.IsMediaType: true;
    fileName        : String      @mandatory;
    size            : Integer;
}

### Get file content
GET http://localhost:4004/odata/v4/admin/Files({{ID}})/content
Authorization: Basic user:password

### Get file content via association
GET http://localhost:4004/odata/v4/admin/MainEntity({{ID}})/file/content
Authorization: Basic user:password

    srv.on('READ', Files, async (req, next) => {
        //if file content is requested, return only file as stream
        if (req.context.req.url.includes('content')) {

            // workaround: when File is requested via Association from MainEntity, as the ID is then not provided directly
            if (req.context.req.url.includes('MainEntity')) {
                req.data.ID = await SELECT.one.from(req.subject).columns('ID')
            }

            const file = await SELECT.from(Files, req.data.ID)
            if (!file) return next() // if file not found, just handover to default handler to get 404 response

            try {
                const stream = await getMyStreamFromExternalSystem(req)
                return [{ value: stream }]
            } catch (err) {
                req.error(`Could not read file content`)
            }

        } else return next() // else delegate to next/default handlers without file content
    })

annotate service.fileservice@(
    UI.FieldGroup #FileGroup      : {
        $Type: 'UI.FieldGroupType',
        Data : [
            {
                $Type: 'UI.DataField',
                label: 'Main ID',
                Value: ID,
            },
            {
                $Type: 'UI.DataField',
                label: 'File ID',
                Value: file.ID,
            },
            {
                $Type: 'UI.DataField',
                Value: file.content,
            },
            {
                $Type: 'UI.DataField',
                Value: file.mediaType,
            },
            {
                $Type: 'UI.DataField',
                Value: file.fileName,
            },
            {
                $Type: 'UI.DataField',
                Value: file.size,
            },
        ],
    },
    UI.Facets                     : [
        {
            $Type : 'UI.ReferenceFacet',
            ID    : 'GeneratedFacet2',
            Label : 'File Information',
            Target: '@UI.FieldGroup#FileGroup',
        },
    ],
);

// Workaround as currently display file content via an association in Fiori Elements is incorrectly trying to fetch the media type.
// Therefore add a fix value for the media type. Of course, this only works, if you only expect a specific file type.
annotate service.Files with {
  @Core.MediaType : 'application/pdf'
  content
};