Hi,
I am getting this persistent error that I can't fix:
> PropertyValueException: not-null property references a null or transient
value
AstroLab.Research.LearningLab.AstroComet._AstroLab.Research.LearningLab.AstroSystem.CometsBackref
This error happens inside Session.Save. I create a new comet
programatically, and I am trying to use Session.Save to persist it to the
database.
Googling the error turns up very little info.
In the database, the two tables look like this:
```
CREATE TABLE cometList (
[systemID] [int] NOT NULL,
[cometID] [int] IDENTITY(1,1) NOT NULL,
[cometName] [nvarchar](255) NOT NULL,
[cometSequence] [int] NOT NULL,
[isLocal] [bit] NULL
);
CREATE TABLE systemList (
[learningID] [int] NOT NULL,
[systemID] [int] IDENTITY(1,1) NOT NULL,
[systemSequence] [int] NOT NULL,
[systemName] [nvarchar](255) NULL,
[systemDateTime] [datetime2](0) NULL,
);
```
In the cometList table, the systemID column is a foreign key(systemList).
Inside my .NetCore Web App, my AstroComet XML mapping looks like this:
```
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
schema="dbo" assembly="AstroLab.Learn"
namespace="AstroLab.Research.LearningLab">
<class name="AstroComet" table="cometList">
<id name="Id" column="cometID">
<generator class="identity" />
</id>
<many-to-one name="System" class="AstroSystem" column="systemID"
update="false" insert="false" />
<property name="Sequence" column="cometSequence" update="false"
insert="false" />
<property name="Title" column="cometName" />
<property name="IsLocal" column="isLocal"/>
</class>
</hibernate-mapping>
```
And the AstroSystem mapping looks like this:
```
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
schema="dbo" assembly="AstroLab.Learn"
namespace="AstroLab.Research.LearningLab">
<class name="AstroSystem" table="systemList">
<id name="Id" column="systemID">
<generator class="identity" />
</id>
<many-to-one name="LearningLab" class="LearningLab" column="learningID"
insert="false" update="false" />
<property name="Sequence" column="systemSequence" insert="false"
update="false"/>
<property name="Title" column="systemName" />
<property name="ResearchDate" column="systemDateTime" />
<list name="Comets" inverse="false" cascade="all">
<key column="systemID" not-null="true" />
<index column="cometSequence" />
<one-to-many class="AstroComet" />
</list>
</class>
</hibernate-mapping>
```
I've searched, tried a few things, rewrote some of the code, but it always
gives me this error no matter how I try to fix it.
If anyone has any experience with an error like this, please let me know.
Thanks!
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