Misc user docs fixes.
Reviewers: buda, mislav.bradac, teon.banek, florijan Reviewed By: buda Differential Revision: https://phabricator.memgraph.io/D947
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Matej Ferencevic
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@ -30,7 +30,7 @@ types. Following is a table of supported data types.
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-----------|------------
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`Null` | Denotes that the property has no value. This is the same as if the property does not exist.
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`String` | A character string, i.e. text.
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`Boolean` | A Boolean value, either `true` or `false`.
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`Boolean` | A boolean value, either `true` or `false`.
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`Integer` | An integer number.
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`Float` | A floating-point number, i.e. a real number.
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`List` | A list containing any number of property values of any supported type. It can be used to store multiple values under a single property name.
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@ -7,7 +7,7 @@ install the Docker engine on the system. Instructions how to install Docker
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can be found on the
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[official Docker website](https://docs.docker.com/engine/installation).
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Memgraph Docker image was built with Docker version `1.12` and should be
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compatible with all latter versions.
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compatible with all later versions.
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### Docker Import
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@ -124,7 +124,7 @@ All of the parameters can also be found in `/etc/memgraph/memgraph.conf`.
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[^1]: Maximum number of concurrent executions on the current CPU.
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To find more about how to execute queries on Memgraph please proceed to
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[Quick Start](quick-start.md).
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**Quick Start**.
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### Cleanup
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@ -34,18 +34,18 @@ following query.
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Finding connected nodes can be achieved by using the query:
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MATCH (node1) -[connection]- (node2) RETURN node1, connection, node2
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MATCH (node1)-[connection]-(node2) RETURN node1, connection, node2
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In addition to general pattern matching, you can narrow the search down by
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specifying node labels and properties. Similarly, edge types and properties
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can also be specified. For example, finding each node labeled as `Person` and
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with property `age` being 42, is done with the following query.
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MATCH (n :Person {age: 42}) RETURN n.
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MATCH (n :Person {age: 42}) RETURN n
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While their friends can be found with the following.
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MATCH (n :Person {age: 42}) -[:FriendOf]- (friend) RETURN friend.
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MATCH (n :Person {age: 42})-[:FriendOf]-(friend) RETURN friend
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There are cases when a user needs to find data which is connected by
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traversing a path of connections, but the user doesn't know how many
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@ -55,22 +55,21 @@ with *variable path lengths*. Matching such a path is achieved by using the
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traversing from `node1` to `node2` by following any number of connections in a
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single direction can be achieved with:
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MATCH (node1) -[r*]-> (node2) RETURN node1, r, node2
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MATCH (node1)-[r*]->(node2) RETURN node1, r, node2
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If paths are very long, finding them could take a long time. To prevent that,
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a user can provide the minimum and maximum length of the path. For example,
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paths of length between 2 and 4 can be obtained with a query like:
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MATCH (node1) -[r*2..4]-> (node2) RETURN node1, r, node2
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MATCH (node1)-[r*2..4]->(node2) RETURN node1, r, node2
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It is possible to name patterns in the query and return the resulting paths.
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This is especially useful when matching variable length paths:
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MATCH path = () -[r*2..4]-> () RETURN path
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MATCH path = ()-[r*2..4]->() RETURN path
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More details on how `MATCH` works can be found
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[here](https://neo4j.com/docs/developer-manual/current/cypher/clauses/match/).
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Note that *named paths* are not yet supported.
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The `MATCH` clause can be modified by prepending the `OPTIONAL` keyword.
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`OPTIONAL MATCH` clause behaves the same as a regular `MATCH`, but when it
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@ -109,11 +108,11 @@ When you want to get everything that was matched, you can use the `*`
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This query:
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MATCH (node1) -[connection]- (node2) RETURN *
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MATCH (node1)-[connection]-(node2) RETURN *
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is equivalent to:
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MATCH (node1) -[connection]- (node2) RETURN node1, connection, node2
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MATCH (node1)-[connection]-(node2) RETURN node1, connection, node2
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`RETURN` can be followed by the `DISTINCT` operator, which will remove
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duplicate results. For example, getting unique names of people can be achieved
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@ -230,7 +229,7 @@ You can still use the `RETURN` clause to produce results after writing, but it
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is not mandatory.
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Details on which kind of data can be stored in *Memgraph* can be found in
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[Storable Data Types](data-types.md) chapter.
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**Storable Data Types** chapter.
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#### CREATE
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@ -239,7 +238,7 @@ is done by providing a pattern, similarly to `MATCH` clause.
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For example, to create 2 new nodes connected with a new edge, use this query.
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CREATE (node1) -[:edge_type]-> (node2)
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CREATE (node1)-[:edge_type]->(node2)
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Labels and properties can be set during creation using the same syntax as in
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[MATCH](#match) patterns. For example, creating a node with a label and a
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@ -269,7 +268,7 @@ This clause is used to delete nodes and edges from the database.
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Example. Removing all edges of a single type.
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MATCH () -[edge :type]- () DELETE edge
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MATCH ()-[edge :type]-() DELETE edge
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When testing the database, you want to often have a clean start by deleting
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every node and edge in the database. It is reasonable that deleting each node
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@ -328,7 +327,7 @@ created. In a way, this clause is like a combination of `MATCH` and `CREATE`.
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Example. Ensure that a person has at least one friend.
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MATCH (n :Person) MERGE (n) -[:FriendOf]-> (m)
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MATCH (n :Person) MERGE (n)-[:FriendOf]->(m)
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The clause also provides additional features for updating the values depending
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on whether the pattern was created or matched. This is achieved with `ON
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@ -336,7 +335,7 @@ CREATE` and `ON MATCH` sub clauses.
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Example. Set a different properties depending on what `MERGE` did.
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MATCH (n :Person) MERGE (n) -[:FriendOf]-> (m)
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MATCH (n :Person) MERGE (n)-[:FriendOf]->(m)
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ON CREATE SET m.prop = "created" ON MATCH SET m.prop = "existed"
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For more details, click [this
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@ -409,22 +408,22 @@ a custom implementation, based on the edge expansion syntax.
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Finding the shortest path between nodes can be done using breadth-first
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expansion:
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MATCH (a {id: 723})-[r:Type \*bfs..10]-(b {id : 882}) RETURN *
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MATCH (a {id: 723})-[r:Type *bfs..10]-(b {id: 882}) RETURN *
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The above query will find all paths of length up to 10 between nodes `a` and `b`.
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The edge type and maximum path length are used in the same way like in variable
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length expansion.
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To find only the shortest path, simply append LIMIT 1 to the RETURN clause.
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To find only the shortest path, simply append `LIMIT 1` to the `RETURN` clause.
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MATCH (a {id: 723})-[r:Type \*bfs..10]-(b {id : 882}) RETURN * LIMIT 1
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MATCH (a {id: 723})-[r:Type *bfs..10]-(b {id: 882}) RETURN * LIMIT 1
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Breadth-fist expansion allows an arbitrary expression filter that determines
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if an expansion is allowed. Following is an example in which expansion is
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allowed only over edges whose `x` property is greater then `12` and nodes `y`
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whose property is lesser then `3`:
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MATCH (a {id: 723})-[\*bfs..10 (e, n | e.x > 12 and n.y < 3)]-() RETURN *
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MATCH (a {id: 723})-[*bfs..10 (e, n | e.x > 12 and n.y < 3)]-() RETURN *
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The filter is defined as a lambda function over `e` and `n`, which denote the edge
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and node being expanded over in the breadth first search.
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@ -509,11 +508,11 @@ functions.
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Apart from comparison and concatenation operators openCypher provides special
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string operators for easier matching of substrings:
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Operator | Description
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-----------------|------------
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a STARTS WITH b | Returns true if prefix of string a is equal to string b.
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a ENDS WITH b | Returns true if suffix of string a is equal to string b.
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a CONTAINS b | Returns true if some substring of string a is equal to string b.
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Operator | Description
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-------------------|------------
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`a STARTS WITH b` | Returns true if prefix of string a is equal to string b.
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`a ENDS WITH b` | Returns true if suffix of string a is equal to string b.
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`a CONTAINS b` | Returns true if some substring of string a is equal to string b.
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#### Parameters
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@ -523,7 +522,7 @@ filtering results or similar, while the rest of the query remains the same.
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Parameters allow reusing the same query, but with different parameter values.
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The syntax uses the `$` symbol to designate a parameter name. We don't allow
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old Cypher parameter syntax using curly brace. For example, you can parameterize
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old Cypher parameter syntax using curly braces. For example, you can parameterize
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filtering a node property:
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MATCH (node1 {property: $propertyValue}) RETURN node1
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@ -551,17 +550,17 @@ documentation.
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#### CASE
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Conditional expressions can be expressed in openCypher language by simple and
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generic form of CASE expression. A simple form is used to compare an expression
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generic form of `CASE` expression. A simple form is used to compare an expression
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against multiple predicates. For the first matched predicate result of the
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expression provided after the THEN keyword is returned. If no expression is
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matched value following ELSE is returned is provided, or null if ELSE is not
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expression provided after the `THEN` keyword is returned. If no expression is
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matched value following `ELSE` is returned is provided, or `null` if `ELSE` is not
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used:
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MATCH (n)
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RETURN CASE n.currency WHEN "DOLLAR" THEN "$" WHEN "EURO" THEN "€" ELSE "UNKNOWN" END
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In generic form, you don't provided expression whose value is compared to
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predicates, but you list multiple predicates and the first one that evaluates
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In generic form, you don't need to provide an expression whose value is compared to
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predicates, but you can list multiple predicates and the first one that evaluates
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to true is matched:
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MATCH (n)
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@ -581,7 +580,7 @@ keywords (WHERE, MATCH, COUNT, SUM...).
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#### Unicode Codepoints in String Literal
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Use `\u` followed by 4 hex digits in string literal for UTF-16 codepoint and
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'\U' with 8 hex digits for UTF-32 codepoint in Memgraph.
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`\U` with 8 hex digits for UTF-32 codepoint in Memgraph.
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### Difference from Neo4j's Cypher Implementation
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@ -593,28 +592,20 @@ here (especially subtle semantic ones).
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#### Unsupported Constructs
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Data importing. Memgraph doesn't support Cypher's CSV importing capabilities.
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The `UNION` keyword for merging query results.
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The `FOREACH` language construct for performing an operation on every list element.
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The `CALL` construct for a standalone function call. This can be expressed using
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`RETURN functioncall()`. For example, with Memgraph you can get information about
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the indexes present in the database using the `RETURN indexinfo()` openCypher query.
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Stored procedures.
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Regular expressions for string matching.
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`shortestPath` and `allShortestPaths` functions. `shortestPath` can be expressed using
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Memgraph's breadth-first expansion syntax already described in this document.
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Patterns in expressions. For example, Memgraph doesn't support `size((n)-->())`. Most of the time
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the same functionalities can be expressed differently in Memgraph using `OPTIONAL` expansions,
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function calls etc.
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Map projections such as `MATCH (n) RETURN n {.property1, .property2}`.
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* Data importing. Memgraph doesn't support Cypher's CSV importing capabilities.
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* The `UNION` keyword for merging query results.
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* The `FOREACH` language construct for performing an operation on every list element.
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* The `CALL` construct for a standalone function call. This can be expressed using
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`RETURN functioncall()`. For example, with Memgraph you can get information about
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the indexes present in the database using the `RETURN indexinfo()` openCypher query.
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* Stored procedures.
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* Regular expressions for string matching.
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* `shortestPath` and `allShortestPaths` functions. `shortestPath` can be expressed using
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Memgraph's breadth-first expansion syntax already described in this document.
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* Patterns in expressions. For example, Memgraph doesn't support `size((n)-->())`. Most of the time
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the same functionalities can be expressed differently in Memgraph using `OPTIONAL` expansions,
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function calls etc.
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* Map projections such as `MATCH (n) RETURN n {.property1, .property2}`.
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#### Unsupported Functions
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@ -10,6 +10,14 @@ Memgraph supports the openCypher query language which has been developed by
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vendor-independent standardization process. It's a declarative language
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developed specifically for interaction with graph databases.
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### Multiple-Query Transactions
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Memgraph supports transactions containing multiple queries. In other words,
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one can set an explicit transaction start and stop. All of the queries inside
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will be executed as a single transaction. This means that if a single query
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execution fails, all of the executed queries will be reverted and the
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transaction aborted.
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### Bolt
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Clients connect to Memgraph using the
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@ -46,9 +54,9 @@ neo4j-client bolt://<IP_ADDRESS>:<PORT> --insecure --user u --pass p
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Where `<IP_ADDRESS>` and `<PORT>` should be replaced with the network location
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where Memgraph is reachable. The `--insecure` option specifies that SLL should
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be disabled (Memgraph alpha does not support SSL). `--user` and `--pass`
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parameter values are ignored by Memgraph (alpha is single-user), but need to
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be provided for the client to connect automatically.
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be disabled (Memgraph currently does not support SSL). `--user` and `--pass`
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parameter values are ignored by Memgraph (currently the database is
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single-user), but need to be provided for the client to connect automatically.
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After the client has started it should present a command prompt similar to:
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@ -171,10 +179,10 @@ can be disabled by passing `{encrypted: 'ENCRYPTION_OFF'}` during the driver
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construction.
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Here is an example related to `Node.js`. Memgraph doesn't have integrated
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support for `Web Socket` which is required during the execution in any web
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support for `WebSocket` which is required during the execution in any web
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browser. If you want to run `openCypher` queries from a web browser,
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[websockify](https://github.com/novnc/websockify) has to be up and running.
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Requests from web browsers are wrapped into `Web Socket` messages, and a proxy
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Requests from web browsers are wrapped into `WebSocket` messages, and a proxy
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is needed to handle the overhead. The proxy has to be configured to point out
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to Memgraph's Bolt port and web browser driver has to send requests to the
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proxy port.
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@ -217,23 +225,9 @@ run_query("MATCH (n) DETACH DELETE n", function (result) {
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### Limitations
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Memgraph is currently in alpha stage, and has a number of limitations we plan
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Memgraph is currently in early stage, and has a number of limitations we plan
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to remove in future versions.
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#### Single query length
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The maximum length of a query that can be sent from a driver in Python is
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`16378` characters, from a driver in Java `8184` and from a driver in
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JavaScript `1392` characters.
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#### Multiple-Query Transactions
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Even though Memgraph is a transactional database engine, transactions
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containing multiple queries are not yet supported. In other words, explicit
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transaction start and stop aren't yet supported. A transaction is created and
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committed implicitly for each executed query. If query execution fails, the
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transaction is aborted.
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#### Multiple Users & Authorization
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Memgraph is currently single-user only. There is no way to control user
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@ -248,7 +242,7 @@ Memgraph processes.
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#### Secure Sockets Layer (SSL)
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Secure connections are not supported in alpha. For this reason each client
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Secure connections are not supported. For this reason each client
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driver needs to be configured not to use encryption. Consult driver-specific
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guides for details.
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