Question 229240 in PostgreSQL Question posted in
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Postgresql – Why am I not allowed to perform this migration?

I have a postgres database where I use ef to control my migrations code first.

I currently have this table/class.

public class Notification
{
    [Key]
    public Guid Id { get; set; } = Guid.NewGuid();

    public string ActionType { get; set; } = string.Empty;
    public string ActionElement { get; set; } = string.Empty;
    public string ActionElementType { get; set; } = string.Empty;

    public string Message { get; set; } = string.Empty;

    public User ForUser { get; set; } = new User();
    public User ByUser { get; set; } = new User();

    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
    public bool Seen { get; set; } = false;
    public bool Clicked { get; set; } = false;
}

to this

public class Notification
{
    [Key]
    public Guid Id { get; set; } = Guid.NewGuid();

    public string ActionType { get; set; } = string.Empty;
    public string ActionElement { get; set; } = string.Empty;
    public string ActionElementType { get; set; } = string.Empty;

    //public string Message { get; set; } = string.Empty;
    
    public Message MessageContent { get; set; };

    public User ForUser { get; set; } = new User();
    public User ByUser { get; set; } = new User();

    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
    public bool Seen { get; set; } = false;
    public bool Clicked { get; set; } = false;
}

public record Message
{
    [Key]
    public Guid MessageId { get; set; } = Guid.NewGuid();

    public string MessageContent { get; init; }
    public ImmutableDictionary<string, string> MessageContentProperties { get; init; }
}

which have created this migration file:

///
public partial class changeMessageStringToMessageRecord : Migration
{
///
protected override void Up(MigrationBuilder migrationBuilder)
{
migrationBuilder.DropColumn(
name: "Message",
table: "Notifications");

        migrationBuilder.AlterDatabase()
            .Annotation("Npgsql:PostgresExtension:hstore", ",,")
            .Annotation("Npgsql:PostgresExtension:uuid-ossp", ",,")
            .OldAnnotation("Npgsql:PostgresExtension:uuid-ossp", ",,");

        migrationBuilder.AddColumn<Guid>(
            name: "MessageContentMessageId",
            table: "Notifications",
            type: "uuid",
            nullable: false,
            defaultValue: new Guid("00000000-0000-0000-0000-000000000000"));

        migrationBuilder.CreateTable(
            name: "Message",
            columns: table => new
            {
                MessageId = table.Column<Guid>(type: "uuid", nullable: false, defaultValueSql: "uuid_generate_v4()"),
                MessageContent = table.Column<string>(type: "text", nullable: false),
                MessageContentProperties = table.Column<ImmutableDictionary<string, string>>(type: "hstore", nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_Message", x => x.MessageId);
            });

        migrationBuilder.CreateIndex(
            name: "IX_Notifications_MessageContentMessageId",
            table: "Notifications",
            column: "MessageContentMessageId");

        migrationBuilder.AddForeignKey(
            name: "FK_Notifications_Message_MessageContentMessageId",
            table: "Notifications",
            column: "MessageContentMessageId",
            principalTable: "Message",
            principalColumn: "MessageId",
            onDelete: ReferentialAction.Cascade);
    }

    /// <inheritdoc />
    protected override void Down(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.DropForeignKey(
            name: "FK_Notifications_Message_MessageContentMessageId",
            table: "Notifications");

        migrationBuilder.DropTable(
            name: "Message");

        migrationBuilder.DropIndex(
            name: "IX_Notifications_MessageContentMessageId",
            table: "Notifications");

        migrationBuilder.DropColumn(
            name: "MessageContentMessageId",
            table: "Notifications");

        migrationBuilder.AlterDatabase()
            .Annotation("Npgsql:PostgresExtension:uuid-ossp", ",,")
            .OldAnnotation("Npgsql:PostgresExtension:hstore", ",,")
            .OldAnnotation("Npgsql:PostgresExtension:uuid-ossp", ",,");

        migrationBuilder.AddColumn<string>(
            name: "Message",
            table: "Notifications",
            type: "text",
            nullable: false,
            defaultValue: "");
    }
}

When I apply the migration I get the error message

ALTER TABLE "Notifications" ADD CONSTRAINT "FK_Notifications_Message_MessageContentMessageId" FOREIGN KEY ("MessageContentMessageId") REFERENCES "Message" ("MessageId") ON DELETE CASCADE;
Npgsql.PostgresException (0x80004005): 23503: insert or update on table "Notifications" violates foreign key constraint "FK_Notifications_Message_MessageContentMessageId"

I am not sure I understand the issue here? why is there an foreign key issue here?

Tags:

2

Answers


  1. 0

    Your Notification table likely has a MessageContentMessageId that doesn’t map to a a row with the same MessageId in the Message column.

    If you want a foreign key there, you’ll need to clean up your data.

    For example, in your migration, you can include an update statement to remove everything that can’t be found, by adding a SQL statement to set MessageContentMessageId to NULL for messsages that can’t be found

    You can wrap it in a migrationBuilder.Sql function

    UPDATE Notifications
SET MessageContentMessageId = NULL
FROM Notifications AS n
LEFT JOIN Messages AS m on m.MessageId = n.MessageContentMessageId
WHERE m.MessageId IS NULL
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  2. 0

    The error message you’re getting 23503: insert or update on table "Notifications" violates foreign key constraint "FK_Notifications_Message_MessageContentMessageId" typically indicates that there are rows in the "Notifications" table which do not have corresponding entries in the "Message" table.

    Here’s what’s happening:

    1. You’re adding a new column, MessageContentMessageId, to the Notifications table. This column is a foreign key that references the MessageId column of the Message table.
    2. The migration script sets a default value of new Guid("00000000-0000-0000-0000-000000000000") for the MessageContentMessageId column.
    3. After adding the column, you then proceed to create the Message table and establish the foreign key constraint.
    4. The database checks the constraint and finds that there is no Message with a MessageId of 00000000-0000-0000-0000-000000000000. Hence, any row in the Notifications table with this default value violates the foreign key constraint.

    Here’s how you can solve the issue:

    1. Avoid Setting a Default Value: If you can afford not to have a default value for the foreign key column, you can simply remove the default value setting. This way, the column will be nullable, and you won’t immediately violate the foreign key constraint. However, make sure you populate this column with valid values before inserting or updating in the future.

    2. Use a Temporary Default: If you must set a default value, you can:

      • First, add the Message table.
      • Then, insert a temporary Message with an ID of 00000000-0000-0000-0000-000000000000.
      • Now, add the MessageContentMessageId column with its default value.
      • Create the foreign key.
      • Later, if that Message is not needed, you can safely delete it once all references in the Notifications table have been updated to point to valid messages.

    3. Update the Values Before Enforcing the Foreign Key: Add the column without the foreign key constraint, update its values to valid MessageIds from the Message table, and then add the foreign key constraint.

    You’ll have to choose the approach that best fits your use case.

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