Method Insert

txn.go:183–303

Insert is used to add or update an object into the given table. When updating an object, the obj provided should be a copy rather than a value updated in-place. Modifying values in-place that are already inserted into MemDB is not supported behavior.

(table string, obj interface{})

// than a value updated in-place. Modifying values in-place that are already
// inserted into MemDB is not supported behavior.
func (txn *Txn) Insert(table string, obj interface{}) error {
	if !txn.write {
		return fmt.Errorf("cannot insert in read-only transaction")
	}

	// Get the table schema
	tableSchema, ok := txn.db.schema.Tables[table]
	if !ok {
		return fmt.Errorf("invalid table '%s'", table)
	}

	// Get the primary ID of the object
	idSchema := tableSchema.Indexes[id]
	idIndexer := idSchema.Indexer.(SingleIndexer)
	ok, idVal, err := idIndexer.FromObject(obj)
	if err != nil {
		return fmt.Errorf("failed to build primary index: %v", err)
	}
	if !ok {
		return fmt.Errorf("object missing primary index")
	}

	// Lookup the object by ID first, to see if this is an update
	idTxn := txn.writableIndex(table, id)
	existing, update := idTxn.Get(idVal)

	// On an update, there is an existing object with the given
	// primary ID. We do the update by deleting the current object
	// and inserting the new object.
	for name, indexSchema := range tableSchema.Indexes {
		indexTxn := txn.writableIndex(table, name)

		// Determine the new index value
		var (
			ok   bool
			vals [][]byte
			err  error
		)
		switch indexer := indexSchema.Indexer.(type) {
		case SingleIndexer:
			var val []byte
			ok, val, err = indexer.FromObject(obj)
			vals = [][]byte{val}
		case MultiIndexer:
			ok, vals, err = indexer.FromObject(obj)
		}
		if err != nil {
			return fmt.Errorf("failed to build index '%s': %v", name, err)
		}

		// Handle non-unique index by computing a unique index.
		// This is done by appending the primary key which must
		// be unique anyways.
		if ok && !indexSchema.Unique {
			for i := range vals {
				vals[i] = append(vals[i], idVal...)
			}
		}