Table of Contents Candidate Keys Primary Keys Pseudo Keys Best Practices In pengdows.crud Related Pages

Any combination of one or more columns that uniquely identify a record in a database table. These are the legitimate keys that naturally enforce uniqueness based on real-world meaning.

A primary key is the candidate key you choose to define the record's identity in business terms. This should reflect the "reason for the row's existence."

• Must be NOT NULL
• Must be unique
• Should represent a real-world concept (like a username, SKU, or email)
• Typically defines the clustered index

In pengdows.crud, these are marked using the [PrimaryKey] attribute and may span multiple columns. The system uses them for "where by primary key" logic such as BuildWhereByPrimaryKey().

A pseudo key is a synthetic, usually auto-generated value used strictly to uniquely identify a row. Commonly named Id, UserId, or Guid, this is the key used for foreign key relationships and often as a default lookup.

• May be a GUID, int, or deterministic hash
• Exists only to provide a unique identity — not business meaning
• Usually a single column, marked with [Id]

In pengdows.crud:

• This is the default key used by EntityHelper<T, TID> for CRUD operations
• Only one [Id] property is allowed per class

• Use a real candidate key as the primary key
• Use a pseudo key as a stable unique identifier — useful for foreign keys
• Do not make the pseudo key your primary key — this leads to schema drift and poor indexing
• Define your clustered index on the primary key — the thing queries actually filter on

pengdows.crud enforces this philosophy:

• [Id] marks a unique pseudo key column — single column only
• [PrimaryKey] may be used on one or more fields
• Tables must have a unique single-column [Id] to use the full EntityHelper automation
• BuildWhereByPrimaryKey() and RetrieveByPrimaryKey() target [PrimaryKey] columns instead of [Id]

This allows you to:

• Use deterministic UUIDs as [Id] while still enforcing real-world uniqueness on [PrimaryKey]
• Maintain proper indexing and cardinality
• Keep foreign keys consistent while enforcing business logic

• EntityHelper<TEntity, TRowID>
• SqlContainer
• Supported Databases