I'm trying to create an ER diagram with DataGrip 2019.3 however I get duplication of relationships. Once a "false" relay is only based on keys (t1_id:t1 id) without any foreign keys being set at all, and after creating a foreign key the relation is already duplicated (id:t2_id_fkey id).
I'm using PostgreSQL 12
CREATE TABLE public.t1
(
id integer NOT NULL,
name character varying COLLATE pg_catalog."default",
CONSTRAINT t1_pkey PRIMARY KEY (id)
)
CREATE TABLE public.t2
(
id integer NOT NULL,
t1_id integer NOT NULL,
namne character varying COLLATE pg_catalog."default",
CONSTRAINT t2_pkey PRIMARY KEY (id),
CONSTRAINT t2_id_fkey FOREIGN KEY (id)
REFERENCES public.t1 (id) MATCH SIMPLE
ON UPDATE NO ACTION
ON DELETE NO ACTION
)
In DataGrip 2019.3 the 'fake keys' were introduced. More information is here: https://www.jetbrains.com/help/datagrip/columns.html#foreign-keys
In your case I see two problems.
Fake keys shouldn't be displayed on the diagram by default (but they can be useful). So we will introduce the setting.
Fake keys should disappear from the diagram when the real one is created. We will fix this as well.
So, expect all this in the nearest update. Thanks!
Related
Hope for help because of the following problem. Assume we have a table
CREATE TABLE [dbo].[dummy](
[id] [char](36) NOT NULL,
[name] [varchar](50) NOT NULL
) ON [PRIMARY]
If I create a primary key like this (version 1)
ALTER TABLE dummy ADD CONSTRAINT PK_dummy PRIMARY KEY (ID);
I get a unique name. In this case PK_dummy.
But if I create a primary key like this (version 2)
ALTER TABLE dummy ADD PRIMARY KEY Clustered (ID);
The name changes with every recreation of this primary key.
The format is always PK__dummy__"a dynamic number"
What is the meaning of this number?
And how can I identify primary keys created with version 2 in a hugh database?
Thanks for hints.
What is the meaning of this number?
This depends on product version - it is either based on a unique id or generated randomly.
how can I identify primary keys created with version 2 in a huge database?
SELECT *
FROM sys.key_constraints
WHERE is_system_named = 1
If you don't define the name of a constraint, index, key, etc, SQL Server will give it a name. To ensure uniqueness across the database, it therefore will add "random" characters at the end.
If having a consistent name is important then define the name in your statement, as you did in the first statement.
I've got a very simple relationship between two tables that are used to manage custom UI branding:
ui_portal_branding
CREATE TABLE ui_portal_branding
(
id VARBINARY(16) NOT NULL,
branding_type VARCHAR(128) NOT NULL,
portal_name NVARCHAR(128) NOT NULL,
theme_id VARBINARY(16) NOT NULL,
portal_logo VARBINARY(16) NULL,
portal_favicon VARBINARY(16) NULL,
background_color VARCHAR(50) NULL,
organization_id VARBINARY(16) NULL,
CONSTRAINT pk_ui_port_bran_id PRIMARY KEY (id)
)
ui_portal_resource
CREATE TABLE ui_portal_resource
(
id VARBINARY(16) NOT NULL,
mime_type NVARCHAR(128) NOT NULL,
binary_data VARBINARY(MAX) NOT NULL,
CONSTRAINT pk_ui_port_reso_id PRIMARY KEY (id)
)
Branding is the main table, Resources is a BLOB store for binary data. Both portal_logo and portal_favicon in the branding table are optional binary data from the resource table.
I'd like to define this as a foreign key constraint with the following general logic: neither logo or favicon are required to be defined. If they are defined, they point to a record in the resource table by ui_portal_resource.id. If the data is deleted from the resource table, I want to set the corresponding column in the branding table to null. I don't want to disallow the resource deletion, I don't want to cascade the delete to the branding table.
So I define the following:
ALTER TABLE ui_portal_branding
ADD CONSTRAINT fk_ui_port_bran2ui_port_reso
FOREIGN KEY (portal_logo) REFERENCES ui_portal_resource (id)
ON DELETE SET NULL
So far so good. Now I define:
ALTER TABLE ui_portal_branding
ADD CONSTRAINT fk_ui_port_bran2ui_port_reso2
FOREIGN KEY (portal_favicon) REFERENCES ui_portal_resource (id)
ON DELETE SET NULL
and all of a sudden we have a problem:
Introducing FOREIGN KEY constraint 'fk_ui_port_bran2ui_port_reso2' on table 'ui_portal_branding' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
This to me seems wrong. I'm not introducing a cycle. It's two tables with the foreign keys defined in a single direction. I guess it can technically be multiple cascade paths–if the same resource is the favicon and the logo it has to set 2 things null. But really? This is the deal breaker for the SQL Server engine? Oracle and Postgres both find this situation to be acceptable.
Is there a sensible workaround for this issue? I'm not interested in a solution involving triggers. Is there a better way to model the data? I was hoping that the resources table could service more than just the branding table, which led to the current FK placement. But maybe that is just not possible?
In an Alexander Kuznetsov article, he presents the follow code snippet:
CREATE TABLE dbo.Vehicles(
ID INT NOT NULL,
[Type] VARCHAR(5) NOT NULL,
CONSTRAINT Vehicles_PK PRIMARY KEY(ID),
CONSTRAINT Vehicles_UNQ_ID_Type UNIQUE(ID, [Type]),
CONSTRAINT Vehicles_CHK_ValidTypes CHECK([Type] IN ('Car', 'Truck'))
);
This snippet raises a few questions for me.
Why is it necessary to include both ID and Type in the unique constraint? If just ID is unique, then the combination of the two columns will always be unique as well.
Also, I know how to set a primary key and specify if it unique in SSMS. But how would I specify a primary key on one column, and make a unique constraint on a combination of columns? Does this create two indexes?
This came up because I'm trying to implement similar code, which does not create a composite primary key, and I get the following error. So I'm trying to understand this code better.
The columns in table 'MyTable' do not match an existing primary key or UNIQUE constraint.
EDIT
I was able to get this working by simply creating a composite primary key in MyTable. The actual table definition is shown below. Again, this works. But it is not the same as the code quoted above. And I'm not sure if it would be better if I did it the other way.
CREATE TABLE [dbo].[MessageThread](
[Id] [int] IDENTITY(1,1) NOT NULL,
[MessageThreadType] [int] NOT NULL,
CONSTRAINT [PK_MessageThread_1] PRIMARY KEY CLUSTERED
(
[Id] ASC,
[MessageThreadType] ASC
) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[MessageThread] WITH CHECK ADD CONSTRAINT [CK_MessageThread_ValidType] CHECK (([MessageThreadType]=(2) OR [MessageThreadType]=(1)))
GO
ALTER TABLE [dbo].[MessageThread] CHECK CONSTRAINT [CK_MessageThread_ValidType]
GO
1 : I am not sure of the specific purpose of the given schema. But note that a unique constraint can be applied for multiple reasons, most commonly: (a) to enforce uniqueness and (b) to provide the optimizer with more information to base decisions.
2 : A unique constraint does not create two indexes. It creates a single index with one of the columns as the leading key column. It enforces uniqueness on both. So a unique constraint on a,b could have:
a b
---- ----
1 1
1 2
2 1
2 2
Notice that neither of the columns enforce uniqueness individually. I am not a big fan of using the table designer in SSMS (it has tons of bugs and doesn't support all functionality) but here is how to do it:
a) right-click the grid and choose Indexes/Keys...
b) choose multiple columns using the [...] button in the Columns grid
c) change Type to Unique Key
d) change the Name if desired
Here's an example of a table that already has a primary key. I could add one or more unique indexes if I wanted to:
In my understanding, the reason for unique constraint on ID,[Type] is let detail tables to refer ID,[Type] as foreign key. Usually parent table is required to have unique constraint on columns used for foreign key. For instance, the table in the question can have 2 detail tables:
CREATE TABLE dbo.CARS(
....
vehicle_id INT NOT NULL,
[Type] VARCHAR(5) NOT NULL,
CONSTRAINT CAR_CHK_TYPE CHECK [Type]='Car',
CONSTRAINT CAR_FK_VEHICLE FOREIGN KEY (vehicle_id,[Type]) REFERENCES Vehincle(id,[Type]));
CREATE TABLE dbo.TRUCKS(
....
vehicle_id INT NOT NULL,
[Type] VARCHAR(5) NOT NULL,
CONSTRAINT CAR_CHK_TYPE CHECK [Type]='Truck',
CONSTRAINT CAR_FK_VEHICLE FOREIGN KEY (vehicle_id,[Type]) REFERENCES Vehincle(id,[Type]));
This way Cars will have details only about Car type, whereas TRUCKS only about Truck.
Such design is used to avoid polymorphic relationship, for instance
CREATE TABLE dbo.VEHICLE (
...,
ref_id INT NOT NULL,
-- PK of 'master' table
ref_name VARCHAR(20) NOT NULL,
-- here we put 'truck' or 'car', so we virtually have 2 parents;
-- in this case we cannot use FK constraint, the only thing that may
-- somehow enforce the logical constraint is writing a trigger
Update
Your updated table definition looks good to me. I guess the sample table was initially designed for Oracle and then ported to SQLServer. In Oracle, that unique constraint and primary key can use the same index, so there is no penalty for having both PK and Unique constraint.
Good question. Theoretically you're right; there is no reason, a record can always be uniquely identified by its PK and the unique constraint will always be satisfied as long as this is true. However, if ID and Type have some relationship outside the bounds of the data layer (maybe this table is the data model for an Enum?), then it's unlikely that there would be two different IDs with the same Type because the uniqueness of Type is enforced elsewhere. The constraint also sets up an index that includes both ID and Type, making the table relatively efficient to be queried by that combination of columns.
You set up a unique constraint using the "Manage Indexes and Keys" option. Yes, this will create an index and unique constraint for the primary key, and an index and unique constraint for the combination of PK and Type.
I suspect the reason for having both columns in the UNIQUE constraint is related to the error message you mentioned. SQL Server (in common with other SQL DBMSs) has a limitation that a FOREIGN KEY constraint can only reference exactly the set of columns defined by a uniqueness constraint. So if a FOREIGN KEY constraint references two columns then those two columns must have a uniqueness constraint on them - even if other constraints already guarantee uniqueness. This is a pointless limitation but it is part of standard SQL.
The following example is quite similar and explains why a composite foreign key and nested uniqueness constraints can be useful.
http://consultingblogs.emc.com/davidportas/archive/2007/01/08/Distributed-Keys-and-Disjoint-Subtypes.aspx
Here you go:
Cars and trucks have different attributes, so they do not belong in one table. This is why I have two tables, Cars and Trucks.
Yet cars and trucks share some attributes, such as VIN (vehicle idenification number). More to the point, VIN is unique. This is why I need a table Vehicles. A vehicle cannot be both a car and a truck, so I must make sure it is not possible to enter both (VIN=123456789, Type=Car) and (VIN=123456789, Type=Truck). This is why I have a PK on VIN only.
I must ensure that a vehicle cannot have corresponding rows in both Cars and Trucks tables. This is why I have Type column in Cars and Trucks, and this is why I want (VIN, Type) in child tables Cars and Trucks refer to the parent table Vehicles. The only reason why I need an additional unique constraint on (VIN, Type) is this: it is referred by FK constraints from child tables.
BTW, you could leave a comment on the blog - in that case sqlblog would send me a message. It is a coincidence that I noticed your question here; I was supposed to go skiing, only there is no snow.
I had a lot of trouble implementing the technique described in an Alexander Kuznetsov article. Basically, the article describes a way to create a FK between one table and alternate tables, and still maintain full constraints on those relationship.
Here's part of Alexander's code:
CREATE TABLE dbo.Vehicles(
ID INT NOT NULL,
[Type] VARCHAR(5) NOT NULL,
CONSTRAINT Vehicles_PK PRIMARY KEY(ID),
CONSTRAINT Vehicles_UNQ_ID_Type UNIQUE(ID, [Type]),
CONSTRAINT Vehicles_CHK_ValidTypes CHECK([Type] IN ('Car', 'Truck'))
)
CREATE TABLE dbo.Cars(ID INT NOT NULL,
[Type] AS CAST('Car' AS VARCHAR(5)) PERSISTED,
OtherData VARCHAR(10) NULL,
CONSTRAINT Cars_PK PRIMARY KEY(ID),
CONSTRAINT Cars_FK_Vehicles FOREIGN KEY(ID, [Type])
REFERENCES dbo.Vehicles(ID, [Type])
)
I finally got it working after errors and confirmed bugs. But when I generate my EF models from the new schema, it is missing a relationship between two of my tables.
The problem is that, in order to have a FK on two columns, there must be an index or unique constraint on both those columns. However, in my case, I also have another table with a FK to a single column in the base table (Vehicles, in Alexander's code).
Since you cannot have more than one PK in a table, this means I cannot have a FK to a PK on both sides. The PK can be for one or two columns, and the other FK will need to reference the non-PK unique constraint.
Unfortunately, Entity Framework will only create relationships for you when there is a FK to a PK. That's the problem. Can someone who understand DB design better than I spot any other alternatives here?
Note: I realize some will see the obvious fix as simply modifying the model to manually add the additional relationship. Unfortunately, we are using a database project and are constantly using automated systems to regenerate the project and model from an updated database. So manual steps are really not practical.
You can't have more than one PK, but you can have more than one unique constraint, and in SQL Server you can create a foreign key constraint that references a unique constraint (one or multiple columns). Here is an example of two tables that roughly look like your model.
CREATE TABLE dbo.Vehicles
(
VehicleID INT PRIMARY KEY,
[Type] VARCHAR(5) NOT NULL UNIQUE,
CONSTRAINT u1 UNIQUE(VehicleID, [Type])
);
CREATE TABLE dbo.Cars
(
CarID INT PRIMARY KEY,
VehicleID INT NOT NULL
FOREIGN KEY REFERENCES dbo.Vehicles(VehicleID),
[Type] VARCHAR(5) NOT NULL
FOREIGN KEY REFERENCES dbo.Vehicles([Type]),
CONSTRAINT fk1 FOREIGN KEY (VehicleID, [Type])
REFERENCES dbo.Vehicles(VehicleID, [Type])
);
Note that Cars has three foreign keys: one points to the PK of vehicles (VehicleID), one points to the unique constraint on Vehicles([Type]), and one points to the multi-column unique constraint on Vehicles(VehicleID, [Type]). I realize this is not equivalent to what you are trying to do but should demonstrate that SQL Server, at least, is capable of doing everything you seem to want to do (I'm having a hard time concluding what you're actually because you keep swapping concepts between what Alex did, what you're trying to do but failing, and what you've done successfully).
Are you saying that EF will not recognize a foreign key that references a unique constraint? If so, does that affect constraints that have more than one column, or all unique constraints? If this is the case, that's a shame, because it is certainly supported in SQL Server. Seems like this would either be a bug or an intentional omission (given that the standard doesn't strictly allow FKs against unique constraints). I wonder if there are any bugs reported on Connect?
I have no idea how to force EF to recognize it, but I do know that just about all the people I know who use database projects end up performing pre- or post-deployment modifications and these can be relatively automated.
I have a table called objectives, each objective has zero to many cause-effect relationships with other objectives, these relationships I have to be stored in the database, let me know if there's a way to relate this table records.
There is not a way to relate the records without creating an additional table (you would need N-1 additional columns on your current table to model the N possible effects of a cause).
Creating an additional table like the one below should serve your purpose.
CREATE TABLE cause_effect (
cause integer NOT NULL,
effect integer NOT NULL,
CONSTRAINT cause_effect_pkey PRIMARY KEY (cause, effect),
CONSTRAINT cause_effect_cause_fkey FOREIGN KEY (cause)
REFERENCES yourtable (id),
CONSTRAINT cause_effect_effect_fkey FOREIGN KEY (effect)
REFERENCES yourtable (id)
)
Apply FKey behaviour as applies.