let donateBooksSchema = mongoose.Schema({
    bookId: {
        type: [{ type: Schema.Types.ObjectId, ref: 'Book' }],
        required: true
    },
    userId: {
        type: [{ type: Schema.Types.ObjectId, ref: 'User' }],
        required: true
    },
    status: {
        type: String,
        default: 'donated',
        enum: ['issued', 'available', 'reserved', 'donated'],
        lowercase: true,
        required: true,
    },
    reservedBy: {
        type: [{ type: Schema.Types.ObjectId, ref: 'User' }],
    },
    donationDate: {
        type: Date,
        default: Date.now
    }
});