Data types

We have data in database, the stored data must be typed for our convenience.

Supported types

Type	Code	Type in Python
String	0	str
Number	1	float
Tree	2	dict
Empty	3	None
Boolean	4	bool
Bytes	5	bytes

1. The first column is the type class used by modb internally.

2. The second column is the type code used by modb internally to identify the type of the data read in database binary.

   What is type code

   Your inserted data must be represented as bytes then stored on you file binary. After the data is written as bytes. There should be a type code to help modb to indentify the type of the data comes afterwards.

3. The third column is the type you will get when you do get on Data object. The conversion will be done automatically from Type to Type in Python. For example, if you insert a str-typed data value, your inserted str object will be converted to modb.format.String, and vice versa.

   Note

   Actually you don't need to care about this type conversion, modb will do the conversion automatically for you.

Important

• Unlike value data, the type of inserted key data is limited, only String, Number and Bytes are supported.
• Only one type can be inserted to one node, for example, if you insert str-type key once, then you can not insert other typed data from now on. The value data does not have this limitation.
• For simplicity, this limitation will not be released in near future.

Note about Tree

For Tree in modb, we use dict for inserting, modb.low.VirtualBNode for manipulating.

# for inserting
node.insert(
    key="sub",
    value={
        "a": "b",
        "c": "d",
    }
    # which is `dict` typed
)

# for manipulating
node['sub'].get()
# which is `modb.low.VirtualBNode` typed

Layout in binary

Note

A unsigned 8-bit integer will be followed by concrete bytes data, like so

type code | Data
U8        | vary

String

Your str-typed object will be encoded using utf-8 encoding.

data length | encoded-string
U32         | vary

Number

Using IEEE 754 binary32 conversion.