When importing nodes, several more types can be specified in the header of the
CSV file (along with all property types):
-`ID`: id of the node that should be used as the node ID when importing
relationships
-`LABEL`: designates that the field contains additional labels for the node
-`IGNORE`: designates that the field should be ignored
The `ID` field type sets the internal ID that will be used for the node when
creating relationships. It is optional and nodes that don't have an ID value
specified will be imported, but can't be connected to any relationships. If you
want to save the ID value as a property in the database, just specify a name for
the ID (`user_id:ID`). If you just want to use the ID during the import, leave
out the name of the field (`:ID`). The `ID` field also supports creating
separate ID spaces. The ID space is specified with the ID space name appended
to the `ID` type in parentheses (`ID(user)`). That allows you to have the same
IDs (by value) for multiple different node files (for example, numbers from 1 to
N). The IDs in each ID space will be treated as an independent set of IDs that
don't interfere with IDs in another ID space.
The `LABEL` field type adds additional labels to the node. The value is treated
as an array type so that multiple additional labels can be specified for each
node. The value is split using the array delimiter (`--array-delimiter` flag).
### Relationships
In order to be able to import relationships, you must import the nodes in the
same invocation of `mg_import_csv` that is used to import the relationships.
When importing relationships, several more types can be specified in the header
of the CSV file (along with all property types):
-`START_ID`: id of the start node that should be connected with the
relationship
-`END_ID`: id of the end node that should be connected with the relationship
-`TYPE`: designates the type of the relationship
-`IGNORE`: designates that the field should be ignored
The `START_ID` field type sets the start node that should be connected with the
relationship to the end node. The field *must* be specified and the node ID
must be one of the node IDs that were specified in the node CSV files. The name
of this field is ignored. If the node ID is in an ID space, you can specify the
ID space for the in the same way as for the node ID (`START_ID(user)`).
The `END_ID` field type sets the end node that should be connected with the
relationship to the start node. The field *must* be specified and the node ID
must be one of the node IDs that were specified in the node CSV files. The name
of this field is ignored. If the node ID is in an ID space, you can specify the
ID space for the in the same way as for the node ID (`END_ID(user)`).
The `TYPE` field type sets the type of the relationship. Each relationship
*must* have a relationship type, but it doesn't necessarily need to be specified
in the CSV file, it can also be set externally for the whole CSV file. The name
of this field is ignored.
## CSV Importer Flags
The importer has many command line options that allow you to customize the way
the importer loads your data.
The two main flags that are used to specify the input CSV files are `--nodes`
and `--relationships`. Basic description of these flags is provided in the table
and more detailed explainion can be found further down bellow.
| Flag | Description |
|-----------------------| -------------- |
|`--nodes` | Used to specify CSV files that contain the nodes to the importer. |
|`--relationships` | Used to specify CSV files that contain the relationships to the importer.|
|`--delimiter` | Sets the delimiter that should be used when splitting the CSV fields (default `,`)|
|`--quote` | Sets the quote character that should be used to quote a CSV field (default `"`)|
|`--array-delimiter` | Sets the delimiter that should be used when splitting array values (default `;`)|
|`--id-type` | Specifies which data type should be used to store the supplied <br/> node IDs when storing them as properties (if the field name is supplied). <br/> The supported values are either `STRING` or `INTEGER`. (default `STRING`)|
|`--ignore-empty-strings` | Instructs the importer to treat all empty strings as `Null` values <br/> instead of an empty string value (default `false`)|
|`--ignore-extra-columns` | Instructs the importer to ignore all columns (instead of raising an error) <br/> that aren't specified after the last specified column in the CSV header. (default `false`) |
| `--skip-bad-relationships`| Instructs the importer to ignore all relationships (instead of raising an error) <br/> that refer to nodes that don't exist in the node files. (default `false`) |
|`--skip-duplicate-nodes` | Instructs the importer to ignore all duplicate nodes (instead of raising an error). <br/> Duplicate nodes are nodes that have an ID that is the same as another node that was already imported. (default `false`) |
| `--trim-strings`| Instructs the importer to trim all of the loaded CSV field values before processing them further. <br/> Trimming the fields removes all leading and trailing whitespace from them. (default `false`) |
The `--nodes` and `--relationships` flags are used to specify CSV files that
contain the nodes and relationships to the importer. Multiple files can be
specified in each supplied `--nodes` or `--relationships` flag. Files that are
supplied in one `--nodes` or `--relationships` flag are treated by the CSV
parser as one big CSV file. Only the first line of the first file is parsed for
the CSV header, all other files (and rows) are treated as data. This is useful
when you have a very large CSV file and don't want to edit its first line just
to add a CSV header. Instead, you can specify the header in a separate file
(e.g. `users_header.csv` or `friendships_header.csv`) and have the data intact
in the large file (e.g. `users.csv` or `friendships.csv`). Also, you can supply
additional labels for each set of node files.
The format of `--nodes` flag is:
`[<label>[:<label>]...=]<file>[,<file>][,<file>]...`. Take note that only the
first `<file>` part is mandatory, all other parts of the flag value are
optional. Multiple `--nodes` flags can be supplied to describe multiple sets of
different node files. For the importer to work, at least one `--nodes` flag
*must* be supplied.
The format of `--relationships` flag is: `[<type>=]<file>[,<file>][,<file>]...`.
Take note that only the first `<file>` part is mandatory, all other parts of the
flag value are optional. Multiple `--relationships` flags can be supplied to
describe multiple sets of different relationship files. The `--relationships`
flag isn't mandatory.
## CSV Parser Logic
The CSV parser uses the same logic as the standard Python CSV parser. The data
is parsed in the same way as the following snippet:
```python
import csv
for row in csv.reader(stream, strict=True):
# process 'row'
```
Python uses 'excel' as the default dialect when parsing CSV files and the
default settings for the CSV parser are:
- delimiter: `','`
- doublequote: `True`
- escapechar: `None`
- lineterminator: `'\r\n'`
- quotechar: `'"'`
- skipinitialspace: `False`
The above snippet can be expanded to:
```python
import csv
for row in csv.reader(stream, delimiter=',', doublequote=True,
escapechar=None, lineterminator='\r\n',
quotechar='"', skipinitialspace=False,
strict=True):
# process 'row'
```
For more information about the meaning of the above values, see:
