Project Connections

In this example, we show how to use AequilibraE’s database connections within a project.

References

• The AequilibraE project

See also

Several functions, methods, classes and modules are used in this example:

• aequilibrae.project.project.Project.db_connection()

• aequilibrae.project.project.Project.results_connection()

• aequilibrae.project.project.Project.transit_connection()

# Imports
from uuid import uuid4
from tempfile import gettempdir
from pathlib import Path

import geopandas as gpd
import pandas as pd

from aequilibrae.utils.create_example import create_example

# We create the example project inside our temp folder.
fldr = Path(gettempdir()) / uuid4().hex
project = create_example(fldr, "sioux_falls")

All AequilibraE projects present three types of connections in the form of properties:

• Spatial connection to the project database

• General connection to the results database

• Spatial connection to the transit database

Each connection can be easily accessed as follows:

with project.db_connection as conn:
    matrices = pd.read_sql("SELECT * FROM matrices", conn)

matrices

	name	file_name	cores	procedure	procedure_id	timestamp	description
0	demand_omx	demand.omx	1	None	None	2020-11-24 08:47:18	Original data imported to OMX format
1	demand_mc	demand_mc.omx	3	None	None	2021-02-24 00:51:35	NaN
2	skims	skims.omx	2	None	None	NaN	Example skim
3	demand_aem	demand.aem	1	None	None	2020-11-24 08:46:42	Original data imported to AEM format

As the project database connection is spatial, it can also be used to query spatial data directly.

with project.db_connection as conn:
    nodes = gpd.read_postgis("SELECT zone_id, ST_AsBinary(geometry) geom FROM zones;", con=conn, geom_col="geom", crs=4326)

nodes.head()

	zone_id	geom
0	8	MULTIPOLYGON (((-96.705 43.5611, -96.70333 43....
1	10	MULTIPOLYGON (((-96.72833 43.538, -96.73 43.53...
2	7	MULTIPOLYGON (((-96.685 43.5611, -96.68333 43....
3	12	MULTIPOLYGON (((-96.78333 43.5178, -96.785 43....
4	9	MULTIPOLYGON (((-96.72833 43.54955, -96.73 43....

For accessing both results and transit databases, the procedure is the same.

When you’re done, don’t forget to close the project.

project.close()