blocks|key|4359324|text|您需要使用autoGenerate属性|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4359325|您的主键注释应如下所示：|4359326|@PrimaryKey(autoGenerate+=+true)|code-block|syntax|javascript|4359327|PrimaryKey的参考。|4359328|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.android.com/reference/androidx/room/PrimaryKey#autoGenerate())^0|5|C|0|0|0|0|A|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|10|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|11|8|@]|D|@$9|12|A|13|1|14]]|E|$]]|$1|O|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

You need to use the <code>autoGenerate</code> property

Your primary key annotation should be like this:

<pre><code>@PrimaryKey(autoGenerate = true)
</code></pre>

Reference for <a href="https://developer.android.com/reference/androidx/room/PrimaryKey#autoGenerate()" rel="noreferrer">PrimaryKey</a>.

blocks|key|4359397|text|您可以像这样添加@PrimaryKey(autoGenerate+=+true)：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4359398|@Entity
data+class+Food(
++++++++var+foodName:+String,+
++++++++var+foodDesc:+String,+
++++++++var+protein:+Double,+
++++++++var+carbs:+Double,+
++++++++var+fat:+Double
){
++++@PrimaryKey(autoGenerate+=+true)
++++var+foodId:+Int+=+0+//+or+foodId:+Int?+=+null
++++var+calories:+Double+=+0.toDouble()
}|code-block|syntax|javascript|4359399|entityMap^0|8|W|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

You can add <code>@PrimaryKey(autoGenerate = true)</code> like this:

<pre><code>@Entity
data class Food(
 var foodName: String, 
 var foodDesc: String, 
 var protein: Double, 
 var carbs: Double, 
 var fat: Double
){
 @PrimaryKey(autoGenerate = true)
 var foodId: Int = 0 // or foodId: Int? = null
 var calories: Double = 0.toDouble()
}
</code></pre>

blocks|key|4359165|text|在这么多答案之后，这真是令人难以置信，但我最后做的几乎没有什么不同。我不喜欢主键可以为空，我想让它作为第一个参数，也想在不定义它的情况下插入，而且它也不应该是var。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4359166|@Entity(tableName+=+"employments")
data+class+Employment(
++++@PrimaryKey(autoGenerate+=+true)+val+id:+Long,
++++@ColumnInfo(name+=+"code")+val+code:+String,
++++@ColumnInfo(name+=+"title")+val+name:+String
){
++++constructor(code:+String,+name:+String)+:+this(0,+code,+name)
}|code-block|syntax|javascript|4359167|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Its unbelievable after so many answers, but I did it little differently in the end. I don't like primary key to be nullable, I want to have it as first argument and also want to insert without defining it and also it should not be var.
<pre><code>@Entity(tableName = &quot;employments&quot;)
data class Employment(
 @PrimaryKey(autoGenerate = true) val id: Long,
 @ColumnInfo(name = &quot;code&quot;) val code: String,
 @ColumnInfo(name = &quot;title&quot;) val name: String
){
 constructor(code: String, name: String) : this(0, code, name)
}
</code></pre>

blocks|key|4359149|text|这对我来说很有效：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4359150|@Entity(tableName+=+"note_table")
data+class+Note(
++++@ColumnInfo(name="title")+var+title:+String,
++++@ColumnInfo(name="description")+var+description:+String+=+"",
++++@ColumnInfo(name="priority")+var+priority:+Int,
++++@PrimaryKey(autoGenerate+=+true)+var+id:+Int+=+0//last+so+that+we+don't+have+to+pass+an+ID+value+or+named+arguments
)|code-block|syntax|javascript|4359151|请注意，id是最后一个，以避免在将实体插入到Room之前创建实体时必须使用命名参数。将其添加到房间后，请在更新实体时使用该id。|4359152|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

This works for me:
<pre><code>@Entity(tableName = &quot;note_table&quot;)
data class Note(
 @ColumnInfo(name=&quot;title&quot;) var title: String,
 @ColumnInfo(name=&quot;description&quot;) var description: String = &quot;&quot;,
 @ColumnInfo(name=&quot;priority&quot;) var priority: Int,
 @PrimaryKey(autoGenerate = true) var id: Int = 0//last so that we don't have to pass an ID value or named arguments
)
</code></pre>
Note that the id is last to avoid having to use named arguments when creating the entity, before inserting it into Room. Once it's been added to room, use the id when updating the entity.

blocks|key|4359059|text|例如，如果您想要存储一个带有字段(firstname,+lastname+,+email)的users实体，并且您想要自动生成id，您可以这样做。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4359060|@Entity(tableName+=+"users")
data+class+Users(
+++@PrimaryKey(autoGenerate+=+true)
+++val+id:+Long,
+++val+firstname:+String,
+++val+lastname:+String,
+++val+email:+String
)|code-block|syntax|javascript|4359061|然后，Room将自动生成并自动递增id字段。|4359062|entityMap^0|G|T|1A|5|0|0|H|2|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|N|$]]

For example, if you have a <code>users</code> entity you want to store, with fields <code>(firstname, lastname , email)</code> and you want autogenerated id, you do this.

<pre><code>@Entity(tableName = "users")
data class Users(
 @PrimaryKey(autoGenerate = true)
 val id: Long,
 val firstname: String,
 val lastname: String,
 val email: String
)
</code></pre>

Room will then autogenerate and auto-increment the <code>id</code> field.

blocks|key|4359093|text|@Entity(tableName+=+"user")
data+class+User(

@PrimaryKey(autoGenerate+=+true)++var+id:+Int?,
+++++++var+name:+String,
+++++++var+dob:+String,
+++++++var+address:+String,
+++++++var+gender:+String
)
{
++++constructor():this(null,
++++++++"","","","")
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|4359094|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>@Entity(tableName = "user")
data class User(

@PrimaryKey(autoGenerate = true) var id: Int?,
 var name: String,
 var dob: String,
 var address: String,
 var gender: String
)
{
 constructor():this(null,
 "","","","")
}
</code></pre>

blocks|key|4359172|text|在下面的示例中，当您创建一个新用户时，传递构造函数中的参数。Room会自动生成id。所有用户对象id都已在id设置器中设置为int默认值，因此不要调用setId|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4359173|@Entity
public+class+User+{

++++@PrimaryKey(autoGenerate+=+true)
++++private+int+id;

++++@ColumnInfo(name+=+"full_name")
++++private+String+name;

++++@ColumnInfo(name+=+"phone")
++++private+String+phone;

+++
++++public+User(String+name,+String+phone)+{
++++++++this.name+=+name;
++++++++this.phone+=+phone;
++++}

++++public+void+setId(int+id){
++++++++this.id+=+id;
++++}

}|code-block|syntax|javascript|4359174|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

In the example below when you create a new user pass the parameters as is in the constructor. Room will autogenerate the id. All user object ids are already set to the int default in the id setter so don't call setId
<pre><code>@Entity
public class User {

 @PrimaryKey(autoGenerate = true)
 private int id;

 @ColumnInfo(name = &quot;full_name&quot;)
 private String name;

 @ColumnInfo(name = &quot;phone&quot;)
 private String phone;

 
 public User(String name, String phone) {
 this.name = name;
 this.phone = phone;
 }

 public void setId(int id){
 this.id = id;
 }

}
</code></pre>

blocks|key|4359441|text|用下面的代码注释你的实体类。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4359442|在Java中：|4359443|@PrimaryKey(autoGenerate+=+true)
private+int+id;|code-block|syntax|javascript|4359444|在Kotlin：|4359445|@PrimaryKey(autoGenerate+=+true)
var+id:+Int|4359446|然后，Room将自动生成并自动递增id字段。|4359447|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

Annotate your Entity class with the code below.
In Java:
<pre><code>@PrimaryKey(autoGenerate = true)
private int id;
</code></pre>
In Kotlin:
<pre><code>@PrimaryKey(autoGenerate = true)
var id: Int
</code></pre>
Room will then auto-generate and auto-increment the id field.

I am creating an Entity (<a href="https://developer.android.com/topic/libraries/architecture/room" rel="noreferrer">Room Persistence Library</a>) class Food, where I want to make <code>foodId</code> as autoincrement.
<pre><code>@Entity
class Food(var foodName: String, var foodDesc: String, var protein: Double, var carbs: Double, var fat: Double)
{
 @PrimaryKey
 var foodId: Int = 0
 var calories: Double = 0.toDouble()
}
</code></pre>
How can I set <code>foodId</code> an autoincrement field?

How to make primary key as autoincrement for Room Persistence lib

Kotlin

Java

我正在创建一个实体()类Food，在这个类中，我想将foodId设置为自动增量。@Entityclass Food(var foodName: String, var foodDesc: String, var protein: Double, var carbs: Double, var fat: Double){    @PrimaryKey    var foodId: Int = 0   

问如何将主键作为房间持久化库的自动增量
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