"To retrieve objects from your database, construct a **QuerySet** via a **Manager** on your model class. \n",
"\n",
"A **QuerySet** represents a collection of objects from your database. It can have zero, one or many filters. Filters narrow down the query results based on the given parameters. In SQL terms, a **QuerySet** equates to a **SELECT** statement, and a **filter** is a limiting clause such as **WHERE** or **LIMIT**.\n",
"\n",
"You get a **QuerySet** by using your model’s **Manager**. Each model has at least one Manager, and it’s called **objects** by default.\n",
"\n",
"The simplest way to retrieve objects from a table is to get all of them. To do this, use the **all()** method on a **Manager**:"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"len(NispRawFrame.objects.all())"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"But usually we want to filter the results. For this purpose we can use the **filter** method, both provided by the **Manager** and the **QuerySet**\n",
"\n"
]
},
{
"cell_type": "code",
"execution_count": 6,
"execution_count": null,
"metadata": {},
"outputs": [
"outputs": [],
"source": [
"# Retrieving all frames with observation id 53877 and filter Y\n",
"# and ordering the results by the ditherNumber\n",
"Keyword argument queries – in filter(), etc. – are “AND”ed together. If you need to execute more complex queries (for example, queries with OR statements), you can use **Q objects**."
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"# Now retrieving all frames with observation ids 53877 and 54349 and filter H\n",
"In order to retrive a single object, instead of using **filter** we can use the **get** method. This method returns one object and raise exceptions if no object is found or if multiple objects satisfy the query"
In the following we will create a NispRawFrame object. Since the NispRawFrame must have also a DataCotainer (i.e. a file to reference to), we first create a DataContainer instance.
We can see also that the fields that we have defined as composite fields provide some synctactic sugar when we initialize them with simple dictionaries.
# or we can create the detector starting from the NispRawFrame, using the reversed relationship,
# using again the create method
image.detectors.create(
detectorId="13",
gain=1.0,
readoutNoise=0.0
)
```
%% Output
%% Cell type:markdown id: tags:
## Objects retrieval
To retrieve objects from your database, construct a **QuerySet** via a **Manager** on your model class.
A **QuerySet** represents a collection of objects from your database. It can have zero, one or many filters. Filters narrow down the query results based on the given parameters. In SQL terms, a **QuerySet** equates to a **SELECT** statement, and a **filter** is a limiting clause such as **WHERE** or **LIMIT**.
You get a **QuerySet** by using your model’s **Manager**. Each model has at least one Manager, and it’s called **objects** by default.
The simplest way to retrieve objects from a table is to get all of them. To do this, use the **all()** method on a **Manager**:
%% Cell type:code id: tags:
``` python
len(NispRawFrame.objects.all())
```
%% Cell type:markdown id: tags:
But usually we want to filter the results. For this purpose we can use the **filter** method, both provided by the **Manager** and the **QuerySet**
%% Cell type:code id: tags:
``` python
# Retrieving all frames with observation id 53877 and filter Y
Keyword argument queries – in filter(), etc. – are “AND”ed together. If you need to execute more complex queries (for example, queries with OR statements), you can use **Q objects**.
In order to retrive a single object, instead of using **filter** we can use the **get** method. This method returns one object and raise exceptions if no object is found or if multiple objects satisfy the query
