Project Fields to Return from Query要从查询返回的投影字段

If you do not specify a projection document, the db.collection.find() method returns all fields in the matching documents.如果未指定投影文档，db.collection.find()方法将返回匹配文档中的所有字段。

If you do not specify a projection document, Compass returns all fields in the matching documents.如果未指定投影文档，Compass将返回匹配文档中的所有字段。

If you do not specify a projection filter, the MongoCollection.Find() method returns all fields in the matching documents.

If you do not specify a projection, the com.mongodb.reactivestreams.client.MongoCollection.find method returns all fields in the matching documents.

If you do not specify a projection, the com.mongodb.client.MongoCollection.find method returns all fields in the matching documents.

If you do not specify a projection document, the find() method yields all fields in the matching documents.如果不指定投影文档，find()方法将生成匹配文档中的所有字段。

If you do not specify a projection document, the find() method returns all fields in the matching documents.

If you do not specify a projection document, the find() method returns all fields in the matching documents.

If you do not specify a projection document, the find method returns all fields in the matching documents.

If you do not specify a projection document, the find() method returns all fields in the matching documents.

If you do not specify a projection, the collection.find() method returns all fields in the matching documents.

db.inventory.find( { status: "A" } )

1. Copy the following expression into the Filter field:将以下表达式复制到“筛选器”字段中：

   { status: "A" }

2. Click Find.单击“查找”。

var filter = Builders<BsonDocument>.Filter.Eq("status", "A");
var result = collection.Find(filter).ToList();

cursor, err := coll.Find(
	context.TODO(),
	bson.D{{"status", "A"}},
)

FindPublisher<Document> findPublisher = collection.find(eq("status", "A"));

FindIterable<Document> findIterable = collection.find(eq("status", "A"));

cursor = db.inventory.find({"status": "A"})

const cursor = db.collection('inventory').find({
  status: 'A'
});

$cursor = $db->coll("inventory")->find( { status => "A" } );

$cursor = $db->inventory->find(['status' => 'A']);

cursor = db.inventory.find({"status": "A"})

client[:inventory].find(status: 'A')

var findObservable = collection.find(equal("status", "A"))

db.inventory.find( { status: "A" }, { item: 1, status: 1 } )

1. Copy the following expression into the Filter field:将以下表达式复制到“筛选器”字段中：

   { status: "A" }

2. Click Options to open the additional query options.单击“选项”以打开其他查询选项。

3. Copy the following expression into the Project field:将以下表达式复制到“项目”字段中：

   { item: 1, status: 1 }

4. Click Find.单击“查找”。

var filter = Builders<BsonDocument>.Filter.Eq("status", "A");
var projection = Builders<BsonDocument>.Projection.Include("item").Include("status");
var result = collection.Find<BsonDocument>(filter).Project(projection).ToList();

projection := bson.D{
	{"item", 1},
	{"status", 1},
}

cursor, err := coll.Find(
	context.TODO(),
	bson.D{
		{"status", "A"},
	},
	options.Find().SetProjection(projection),
)

findPublisher = collection.find(eq("status", "A")).projection(include("item", "status"));

To specify a projection document, chain the com.mongodb.client.FindIterable.projection method to the find method. The example uses the com.mongodb.client.model.Projections class to create the projection documents.

findIterable = collection.find(eq("status", "A")).projection(include("item", "status"));

cursor = db.inventory.find({"status": "A"}, {"item": 1, "status": 1})

const cursor = db
  .collection('inventory')
  .find({
    status: 'A'
  })
  .project({ item: 1, status: 1 });

$cursor = $db->coll("inventory")->find(
    { status => "A" }, { projection => { item => 1, status => 1 } }
);

$cursor = $db->inventory->find(
    ['status' => 'A'],
    ['projection' => ['item' => 1, 'status' => 1]]
);

cursor = db.inventory.find({"status": "A"}, {"item": 1, "status": 1})

client[:inventory].find({ status: 'A' },
                       projection: { item: 1, status: 1 })

findObservable = collection.find(equal("status", "A")).projection(include("item", "status"))

db.inventory.find( { status: "A" }, { item: 1, status: 1, _id: 0 } )

1. Copy the following expression into the Filter field:将以下表达式复制到“筛选器”字段中：

   { status: "A" }

2. Click Options to open the additional query options.单击“选项”以打开其他查询选项。

3. Copy the following expression into the Project field:将以下表达式复制到“项目”字段中：

   { item: 1, status: 1, _id: 0 }

4. Click Find.单击“查找”。

var filter = Builders<BsonDocument>.Filter.Eq("status", "A");
var projection = Builders<BsonDocument>.Projection.Include("item").Include("status").Exclude("_id");
var result = collection.Find<BsonDocument>(filter).Project(projection).ToList();

projection := bson.D{
	{"item", 1},
	{"status", 1},
	{"_id", 0},
}

cursor, err := coll.Find(
	context.TODO(),
	bson.D{
		{"status", "A"},
	},
	options.Find().SetProjection(projection),
)

findPublisher = collection.find(eq("status", "A"))
        .projection(fields(include("item", "status"), excludeId()));

To specify a projection document, chain the com.mongodb.client.FindIterable.projection method to the find method. The example uses the com.mongodb.client.model.Projections class to create the projection documents.

findIterable = collection.find(eq("status", "A"))
        .projection(fields(include("item", "status"), excludeId()));

cursor = db.inventory.find({"status": "A"}, {"item": 1, "status": 1, "_id": 0})

const cursor = db
  .collection('inventory')
  .find({
    status: 'A'
  })
  .project({ item: 1, status: 1, _id: 0 });

$cursor = $db->coll("inventory")->find(
    { status => "A" }, { projection => { item => 1, status => 1, "_id" => 0 } }
);

$cursor = $db->inventory->find(
    ['status' => 'A'],
    ['projection' => ['item' => 1, 'status' => 1, '_id' => 0]]
);

cursor = db.inventory.find({"status": "A"}, {"item": 1, "status": 1, "_id": 0})

client[:inventory].find({ status: 'A' },
                        projection: { item: 1, status: 1, _id: 0 })

findObservable = collection.find(equal("status", "A"))
  .projection(fields(include("item", "status"), excludeId()))

db.inventory.find( { status: "A" }, { status: 0, instock: 0 } )

1. Copy the following expression into the Filter field:将以下表达式复制到“筛选器”字段中：

   { status: "A" }

2. Click Options to open the additional query options.单击“选项”以打开其他查询选项。

3. Copy the following expression into the Project field:将以下表达式复制到“项目”字段中：

   { status: 0, instock: 0 }

4. Click Find.单击“查找”。

var filter = Builders<BsonDocument>.Filter.Eq("status", "A");
var projection = Builders<BsonDocument>.Projection.Exclude("status").Exclude("instock");
var result = collection.Find<BsonDocument>(filter).Project(projection).ToList();

projection := bson.D{
	{"status", 0},
	{"instock", 0},
}

cursor, err := coll.Find(
	context.TODO(),
	bson.D{
		{"status", "A"},
	},
	options.Find().SetProjection(projection),
)

findPublisher = collection.find(eq("status", "A")).projection(exclude("item", "status"));

To specify a projection document, chain the com.mongodb.client.FindIterable.projection method to the find method. The example uses the com.mongodb.client.model.Projections class to create the projection documents.

findIterable = collection.find(eq("status", "A")).projection(exclude("item", "status"));

cursor = db.inventory.find({"status": "A"}, {"status": 0, "instock": 0})

const cursor = db
  .collection('inventory')
  .find({
    status: 'A'
  })
  .project({ status: 0, instock: 0 });

$cursor = $db->coll("inventory")->find(
    { status => "A" }, { projection => { status => 0, instock => 0 } }
);

$cursor = $db->inventory->find(
    ['status' => 'A'],
    ['projection' => ['status' => 0, 'instock' => 0]]
);

cursor = db.inventory.find({"status": "A"}, {"status": 0, "instock": 0})

client[:inventory].find({ status: 'A' },
                        projection: { status: 0, instock: 0 })

findObservable = collection.find(equal("status", "A")).projection(exclude("item", "status"))

db.inventory.find(
   { status: "A" },
   { item: 1, status: 1, "size.uom": 1 }
)

1. Copy the following expression into the Filter field:将以下表达式复制到“筛选器”字段中：

   { status: "A" }

2. Click Options to open the additional query options.单击“选项”以打开其他查询选项。

3. Copy the following expression into the Project field:将以下表达式复制到“项目”字段中：

   { item: 1, status: 1, "size.uom": 1 }

4. Click Find.单击“查找”。

var filter = Builders<BsonDocument>.Filter.Eq("status", "A");
var projection = Builders<BsonDocument>.Projection.Include("item").Include("status").Include("size.uom");
var result = collection.Find<BsonDocument>(filter).Project(projection).ToList();

projection := bson.D{
	{"item", 1},
	{"status", 1},
	{"size.uom", 1},
}

cursor, err := coll.Find(
	context.TODO(),
	bson.D{
		{"status", "A"},
	},
	options.Find().SetProjection(projection),
)

findPublisher = collection.find(eq("status", "A")).projection(include("item", "status", "size.uom"));

To specify a projection document, chain the com.mongodb.client.FindIterable.projection method to the find method. The example uses the com.mongodb.client.model.Projections class to create the projection documents.

findIterable = collection.find(eq("status", "A")).projection(include("item", "status", "size.uom"));

cursor = db.inventory.find({"status": "A"}, {"item": 1, "status": 1, "size.uom": 1})

const cursor = db
  .collection('inventory')
  .find({
    status: 'A'
  })
  .project({ item: 1, status: 1, 'size.uom': 1 });

$cursor = $db->coll("inventory")->find(
    { status => "A" }, { projection => { item => 1, status => 1, "size.uom" => 1 } }
);

$cursor = $db->inventory->find(
    ['status' => 'A'],
    ['projection' => ['item' => 1, 'status' => 1, 'size.uom' => 1]]
);

cursor = db.inventory.find({"status": "A"}, {"item": 1, "status": 1, "size.uom": 1})

client[:inventory].find({ status: 'A' },
                        projection: { 'item' => 1, 'status' => 1, 'size.uom' => 1 })

findObservable = collection.find(equal("status", "A")).projection(include("item", "status", "size.uom"))

db.inventory.find(
   { status: "A" },
   { "size.uom": 0 }
)

1. Copy the following expression into the Filter field:将以下表达式复制到“筛选器”字段中：

   { status: "A" }

2. Click Options to open the additional query options.单击“选项”以打开其他查询选项。

3. Copy the following expression into the Project field:将以下表达式复制到“项目”字段中：

   { "size.uom": 0 }

4. Click Find.单击“查找”。

var filter = Builders<BsonDocument>.Filter.Eq("status", "A");
var projection = Builders<BsonDocument>.Projection.Exclude("size.uom");
var result = collection.Find<BsonDocument>(filter).Project(projection).ToList();

projection := bson.D{
	{"size.uom", 0},
}

cursor, err := coll.Find(
	context.TODO(),
	bson.D{
		{"status", "A"},
	},
	options.Find().SetProjection(projection),
)

findPublisher = collection.find(eq("status", "A")).projection(exclude("size.uom"));

To specify a projection document, chain the com.mongodb.client.FindIterable.projection method to the find method. The example uses the com.mongodb.client.model.Projections class to create the projection documents.

findIterable = collection.find(eq("status", "A")).projection(exclude("size.uom"));

cursor = db.inventory.find({"status": "A"}, {"size.uom": 0})

const cursor = db
  .collection('inventory')
  .find({
    status: 'A'
  })
  .project({ 'size.uom': 0 });

$cursor = $db->coll("inventory")->find(
    { status => "A" }, { projection => { "size.uom" => 0 } }
);

$cursor = $db->inventory->find(
    ['status' => 'A'],
    ['projection' => ['size.uom' => 0]]
);

cursor = db.inventory.find({"status": "A"}, {"size.uom": 0})

client[:inventory].find({ status: 'A' },
                        projection: { 'size.uom' => 0 })

findObservable = collection.find(equal("status", "A")).projection(exclude("size.uom"))

db.inventory.find( { status: "A" }, { item: 1, status: 1, "instock.qty": 1 } )

1. Copy the following expression into the Filter field:将以下表达式复制到“筛选器”字段中：

   { status: "A" }

2. Click Options to open the additional query options.单击“选项”以打开其他查询选项。

3. Copy the following expression into the Project field:将以下表达式复制到“项目”字段中：

   { item: 1, status: 1, "instock.qty": 1 }

4. Click Find.单击“查找”。

var filter = Builders<BsonDocument>.Filter.Eq("status", "A");
var projection = Builders<BsonDocument>.Projection.Include("item").Include("status").Include("instock.qty");
var result = collection.Find<BsonDocument>(filter).Project(projection).ToList();

projection := bson.D{
	{"item", 1},
	{"status", 1},
	{"instock.qty", 1},
}

cursor, err := coll.Find(
	context.TODO(),
	bson.D{
		{"status", "A"},
	},
	options.Find().SetProjection(projection),
)

findPublisher = collection.find(eq("status", "A")).projection(include("item", "status", "instock.qty"));

To specify a projection document, chain the com.mongodb.client.FindIterable.projection method to the find method. The example uses the com.mongodb.client.model.Projections class to create the projection documents.

findIterable = collection.find(eq("status", "A")).projection(include("item", "status", "instock.qty"));

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.对于包含数组的字段，MongoDB提供了以下用于操作数组的投影运算符：$elemMatch、$slice和$。

The following example uses the $slice projection operator to return the last element in the instock array:以下示例使用$slice投影运算符返回instock数组中的最后一个元素：

findIterable = collection.find(eq("status", "A"))
        .projection(fields(include("item", "status"), slice("instock", -1)));

$elemMatch, $slice, and $ are the only way to project specific elements to include in the returned array. $elemMatch、$slice和$是将特定元素投影到返回数组中的唯一方法。For instance, you cannot project specific array elements using the array index; e.g. include("instock.0") projection will not project the array with the first element.例如，不能使用数组索引投影特定的数组元素；include("instock.0")投影将不会投影具有第一个元素的数组。

const cursor = db
  .collection('inventory')
  .find({
    status: 'A'
  })
  .project({ item: 1, status: 1, 'instock.qty': 1 });

$cursor = $db->coll("inventory")->find( { status => "A" },
    { projection => { item => 1, status => 1, "instock.qty" => 1 } } );

$cursor = $db->inventory->find(
    ['status' => 'A'],
    ['projection' => ['item' => 1, 'status' => 1, 'instock.qty' => 1]]
);

cursor = db.inventory.find({"status": "A"}, {"item": 1, "status": 1, "instock.qty": 1})

client[:inventory].find({ status: 'A' },
                        projection: {'item' => 1, 'status' => 1, 'instock.qty' => 1 })

findObservable = collection.find(equal("status", "A")).projection(include("item", "status", "instock.qty"))

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.对于包含数组的字段，MongoDB提供了以下用于操作数组的投影运算符：$elemMatch、$slice和$。

The following example uses the $slice projection operator to return the last element in the instock array:以下示例使用$slice投影运算符返回instock数组中的最后一个元素：

db.inventory.find( { status: "A" }, { item: 1, status: 1, instock: { $slice: -1 } } )

$elemMatch, $slice, and $ are the only way to project specific elements to include in the returned array. $elemMatch、$slice和$是将特定元素投影到返回数组中的唯一方法。For instance, you cannot project specific array elements using the array index; e.g. { "instock.0": 1 } projection will not project the array with the first element.例如，不能使用数组索引投影特定的数组元素；例如{ "instock.0": 1 }投影将不会投影具有第一个元素的数组。

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.对于包含数组的字段，MongoDB提供了以下用于操作数组的投影运算符：$elemMatch、$slice和$。

The following example uses the $slice projection operator to return the last element in the instock array:以下示例使用$slice投影运算符返回instock数组中的最后一个元素：

1. Copy the following expression into the Filter field:将以下表达式复制到“筛选器”字段中：

   { status: "A" }

2. Click Options to open the additional query options.单击“选项”以打开其他查询选项。

3. Copy the following expression into the Project field:将以下表达式复制到“项目”字段中：

   { item: 1, status: 1, instock: { $slice: -1 } }

4. Click Find.单击“查找”。

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.

The following example uses the $slice projection operator to return the last element in the instock array:

var filter = Builders<BsonDocument>.Filter.Eq("status", "A");
var projection = Builders<BsonDocument>.Projection.Include("item").Include("status").Slice("instock", -1);
var result = collection.Find<BsonDocument>(filter).Project(projection).ToList();

$elemMatch, $slice, and $ are the only way to project specific elements to include in the returned array.

For example, the following operation will not project the array with the first element:例如，以下操作将不会投影具有第一个元素的数组：

Builders<BsonDocument>.Projection.Include("instock.0")

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.

The following example uses the $slice projection operator to return the last element in the instock array:

projection := bson.D{
	{"item", 1},
	{"status", 1},
	{"instock", bson.D{
		{"$slice", -1},
	}},
}

cursor, err := coll.Find(
	context.TODO(),
	bson.D{
		{"status", "A"},
	},
	options.Find().SetProjection(projection),
)

$elemMatch, $slice, and $ are the only way to project specific elements to include in the returned array. For instance, you cannot project specific array elements using the array index; e.g. include("instock.0") projection will not project the array with the first element.

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.

The following example uses the $slice projection operator to return the last element in the instock array:

findPublisher = collection.find(eq("status", "A"))
        .projection(fields(include("item", "status"), slice("instock", -1)));

$elemMatch, $slice, and $ are the only way to project specific elements to include in the returned array. For instance, you cannot project specific array elements using the array index; e.g. include("instock.0") projection will not project the array with the first element.

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.

The following example uses the $slice projection operator to return the last element in the instock array:

To specify a projection document, chain the com.mongodb.client.FindIterable.projection method to the find method. The example uses the com.mongodb.client.model.Projections class to create the projection documents.

findIterable = collection.find(eq("status", "A"))
        .projection(fields(include("item", "status"), slice("instock", -1)));

$elemMatch, $slice, and $ are the only way to project specific elements to include in the returned array. For instance, you cannot project specific array elements using the array index; e.g. include("instock.0") projection will not project the array with the first element.

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.对于包含数组的字段，MongoDB提供了以下用于操作数组的投影运算符：$elemMatch、$slice和$。

The following example uses the $slice projection operator to return the last element in the instock array:以下示例使用$slice投影运算符返回instock数组中的最后一个元素：

const cursor = db
  .collection('inventory')
  .find({
    status: 'A'
  })
  .project({ item: 1, status: 1, instock: { $slice: -1 } });

$elemMatch, $slice, and $ are the only way to project specific elements to include in the returned array. $elemMatch、$slice和$是将特定元素投影到返回数组中的唯一方法。For instance, you cannot project specific array elements using the array index; e.g. { "instock.0": 1 } projection will not project the array with the first element.例如，不能使用数组索引投影特定的数组元素；例如{ "instock.0": 1 }投影将不会投影具有第一个元素的数组。

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.

The following example uses the $slice projection operator to return the last element in the instock array:

$cursor = $db->coll("inventory")->find(
    { status => "A" },
    { projection => { item => 1, status => 1, instock => { '$slice' => -1 } } }
);

$elemMatch, $slice, and $ are the only way to project specific elements to include in the returned array. For instance, you cannot project specific array elements using the array index; e.g. { "instock.0" => 1 } projection will not project the array with the first element.

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.

The following example uses the $slice projection operator to return the last element in the instock array:

$cursor = $db->inventory->find(
    ['status' => 'A'],
    ['projection' => ['item' => 1, 'status' => 1, 'instock' => ['$slice' => -1]]]
);

$elemMatch, $slice, and $ are the only way to project specific elements to include in the returned array. For instance, you cannot project specific array elements using the array index; e.g. [ "instock.0" => 1 ] projection will not project the array with the first element.

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.

The following example uses the $slice projection operator to return the last element in the instock array:

cursor = db.inventory.find(
    {"status": "A"}, {"item": 1, "status": 1, "instock": {"$slice": -1}}
)

$elemMatch, $slice, and $ are the only way to project specific elements to include in the returned array. For instance, you cannot project specific array elements using the array index; e.g. { "instock.0": 1 } projection will not project the array with the first element.

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.

The following example uses the $slice projection operator to return the last element in the instock array:

client[:inventory].find({ status: 'A' },
                        projection: {'item' => 1,
                                     'status' => 1,
                                     'instock' => { '$slice' => -1 } })

$elemMatch, $slice, and $ are the only way to project specific elements to include in the returned array. For instance, you cannot project specific array elements using the array index; e.g. { "instock.0" => 1 } projection will not project the array with the first element.

For fields that contain arrays, MongoDB provides the following projection operators for manipulating arrays: $elemMatch, $slice, and $.

The following example uses the $slice projection operator to return the last element in the instock array:

findObservable = collection.find(equal("status", "A"))
  .projection(fields(include("item", "status"), slice("instock", -1)))

$elemMatch, $slice, and $ are the only way to project specific elements to include in the returned array. For instance, you cannot project specific array elements using the array index; e.g. include("instock.0") projection will not project the array with the first element.