MergeOption Enum
Definition
Important
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Specifies how objects being loaded into the object context are merged with objects already in the object context.
public enum class MergeOptionpublic enum MergeOptiontype MergeOption = Public Enum MergeOption- Inheritance
Fields
| Name | Value | Description |
|---|---|---|
| AppendOnly | 0 | Objects that do not exist in the object context are attached to the context. If an object is already in the context, the current and original values of object's properties in the entry are not overwritten with data source values. The state of the object's entry and state of properties of the object in the entry do not change. AppendOnly is the default merge option. |
| OverwriteChanges | 1 | Objects that do not exist in the object context are attached to the context. If an object is already in the context, the current and original values of object's properties in the entry are overwritten with data source values. The state of the object's entry is set to Unchanged, no properties are marked as modified. |
| PreserveChanges | 2 | Objects that do not exist in the object context are attached to the context. |
| NoTracking | 3 | Objects are maintained in a Detached state and are not tracked in the ObjectStateManager. However, Entity Framework-generated entities and POCO entities with proxies maintain a reference to the object context to facilitate loading of related objects. |
Remarks
Entity Framework only maintains a single instance of an object with a specific entity key in the cache. The EntityKey objects are immutable objects that represent object's identity. Entity keys are used to perform identity resolution in the object context. For more information, see Working with Entity Keys. If an entity with the same identity is already being tracked, the data coming from the data source and the data already in the state manager are merged according to the MergeOption of the query.
Additional information on MergeOption.PreserveChanges
If the state of the entity is EntityState.Unchanged, the current and original values in the entry are overwritten with data source values. The state of the entity remains EntityState.Unchanged and no properties are marked as modified.
If the state of the entity is EntityState.Modified, the current values of modified properties are not overwritten with data source values. The original values of unmodified properties are overwritten with the values from the data source.
In .NET Framework 4, Entity Framework compares the current values of unmodified properties with the values that were returned from the data source. If the values are not the same, the property is marked as modified.
Only modified properties are persisted to the data source when you call ObjectContext.SaveChanges.
