var emptyUser User
	var err error
	// belongs to
	err = DB.Model(&emptyUser).Association("Company").Delete(&user1.Company)
	AssertEqual(t, err, gorm.ErrPrimaryKeyRequired)
	// has many
	err = DB.Model(&emptyUser).Association("Pets").Delete(&user1.Pets)
	AssertEqual(t, err, gorm.ErrPrimaryKeyRequired)
	// has one
	err = DB.Model(&emptyUser).Association("Account").Delete(&user1.Account)

### Memory per Process { #memory-per-process }

Now, when the program loads things in memory, for example, a machine learning model in a variable, or the contents of a large file in a variable, all that **consumes a bit of the memory (RAM)** of the server.

	if db5.Error != nil {
		t.Errorf("Should not raise error for join where identical fields in different tables. Error: %s", db5.Error.Error())
	}

    return InvalidatableSet.of(
        set, () -> nodes().contains(node), () -> String.format(NODE_REMOVED_FROM_GRAPH, node));
  }

  protected final <T> Set<T> nodePairInvalidatableSet(Set<T> set, N nodeU, N nodeV) {
    return InvalidatableSet.of(
        set,
        () -> nodes().contains(nodeU) && nodes().contains(nodeV),
        () -> String.format(NODE_PAIR_REMOVED_FROM_GRAPH, nodeU, nodeV));

	var name string
	var total int
	if err := DB.Model(&User{}).Select("name, sum(age)").Where("name = ?", "groupby").Group("name").Row().Scan(&name, &total); err != nil {
		t.Errorf("no error should happen, but got %v", err)
	}

	if name != "groupby" || total != 60 {
		t.Errorf("name should be groupby, but got %v, total should be 60, but got %v", name, total)
	}

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    assertThat(networkAsMutableNetwork.nodes()).contains(N1);
  }

  @Test
  public void addNode_existingNode() {
    assume().that(graphIsMutable()).isTrue();

    addNode(N1);
    ImmutableSet<Integer> nodes = ImmutableSet.copyOf(networkAsMutableNetwork.nodes());
    assertFalse(networkAsMutableNetwork.addNode(N1));
    assertThat(networkAsMutableNetwork.nodes()).containsExactlyElementsIn(nodes);
  }

    for (Integer node : graph.nodes()) {
      new EqualsTester()
          .addEqualityGroup(
              graph.predecessors(node), graph.successors(node), graph.adjacentNodes(node))
          .testEquals();
    }
  }

  @Override
  @Test
  public void nodes_checkReturnedSetMutability() {
    assume().that(graphIsMutable()).isTrue();

    Set<Integer> nodes = graph.nodes();

# Status Codes

You can import the `status` module from `fastapi`:

```python
from fastapi import status
```

`status` is provided directly by Starlette.

It contains a group of named constants (variables) with integer status codes.

For example:

* 200: `status.HTTP_200_OK`
* 403: `status.HTTP_403_FORBIDDEN`
* etc.

  /** Constructor for use by subclasses. */
  public AbstractValueGraph() {}

  @Override
  public Graph<N> asGraph() {
    return new AbstractGraph<N>() {
      @Override
      public Set<N> nodes() {
        return AbstractValueGraph.this.nodes();
      }

      @Override
      public Set<EndpointPair<N>> edges() {
        return AbstractValueGraph.this.edges();
      }

      @Override
      public boolean isDirected() {